Vulnerability-Lookup

GHSA-C29M-XWM3-CM6R

Vulnerability from github – Published: 2026-09-30 15:03 – Updated: 2026-09-30 15:03

Summary

Axios: ReDoS in fromDataURI data: URL parser freezes the Node event loop (DoS)

Details

Summary

Axios for Node.js parses data: URLs in lib/helpers/fromDataURI.js. The current RFC-2397 parser uses a regular expression whose media type groups allow / inside both sides of the type/subtype match. A malformed data: URL containing many slashes and no comma forces the JavaScript regex engine to try many possible placements for the separator before failing.

Applications are affected when they pass untrusted URL strings to axios and do not reject or constrain data: URLs before axios parses them.

Impact

An attacker can make the Node.js event loop spend significant synchronous CPU time parsing a single malformed URL. In a server that accepts a URL from an HTTP request and calls axios.get(url), this can block unrelated requests and health checks until parsing completes.

The issue is availability-only. It does not disclose data or modify requests.

Affected Functionality

Affected:

Node.js HTTP adapter data URL handling.
axios.get() or equivalent calls where config.url has the data: protocol.

Not affected:

Browser fetch/XHR URL handling.
Node requests where the application rejects data: URLs before calling axios.
Older checked 0.x data URL parser shape unless separately proven vulnerable.

Technical Details

lib/helpers/fromDataURI.js contains:

const DATA_URL_PATTERN = /^([^,;]+\/[^,;]+)?((?:;[^,;=]+=[^,;]+)*)(;base64)?,([\s\S]*)$/;

The [^,;]+ groups include /, so a long string of slashes without a comma can be partitioned around the required \/ in many ways before the match fails. The match runs before axios can apply request timeout behavior, so timeout does not mitigate the parsing pause.

Local timing on axios 1.18.1 with small payloads showed about 2.4 ms at 1000 slashes, 16.6 ms at 3000 slashes, and 71.5 ms at 6000 slashes, consistent with the submitted quadratic scaling while avoiding long-running payloads.

Proof of Concept of Attack

Constrained helper-level demonstration:

import axios from 'axios';

await axios.get('data:' + '/'.repeat(6000));

The request fails after parsing, but the failure is delayed by synchronous regex work. Larger payloads increase the pause substantially.

Workarounds

Reject data: URLs before passing untrusted input to axios, or enforce a strict maximum URL length for URL-fetching endpoints. Applications that do not need data: URL support should deny that protocol explicitly.

Original report

# ReDoS in `fromDataURI` data: URL parser freezes the event loop (DoS) ## Affected - Package: `axios` (Node.js http adapter) - Versions: 1.x (regex present on `v1.x`, current release line) - File: `lib/helpers/fromDataURI.js` - CWE-1333 (Inefficient Regular Expression Complexity) ## Issue `fromDataURI` parses `data:` URLs with this regex:

// lib/helpers/fromDataURI.js:9
const DATA_URL_PATTERN = /^([^,;]+\/[^,;]+)?((?:;[^,;=]+=[^,;]+)*)(;base64)?,([\s\S]*)$/;

The mediatype tokens `[^,;]+` include `/`, so they can span multiple slashes ambiguously. A `data:` URL made of many slashes with no comma forces the engine to try every way to place the single `\/` divider before failing — quadratic O(n²) backtracking. It runs synchronously on the main thread, so the whole Node event loop is frozen for the entire parse. Reachable through the public API on the Node http adapter (`axios.get(url)`); the browser fetch/xhr adapters are not affected because they do not call `fromDataURI`. A configured `timeout` does not help: the freeze happens during parsing, before any network timer can fire. ## PoC (minimal)

import axios from 'axios';
// ~256 KB data: URL of pure slashes, no comma
await axios.get('data:' + '/'.repeat(262139)); // blocks the event loop ~6 min, then throws

## Lab results Single-threaded "fetch a user-supplied URL" service (link-preview style) calling `axios.get` on a JSON body `{ "url": "..." }`, with `timeout: 1000` set. Scaling is clean O(n²) (constant k ≈ 5.6e-6 ms/byte², stable across sizes): | data: URL size | Event-loop freeze (one request) | | --- | --- | | 32 KB | 6.3 s (measured end-to-end; server logged `event loop BLOCKED for 6.30s`) | | 64 KB | ~24 s | | 128 KB | ~96 s | | 256 KB | ~385 s (~6.4 min) | | 1 MB | ~100 min | During the freeze the server answers nothing: a `/healthz` liveness probe times out for the whole window, and the server's own event-loop monitor cannot even log until the parse finishes. In a run through an intercepting proxy, the proxy hit its 120 s upstream timeout and gave up, while the origin stayed pegged at 100% CPU on one core past that — client/proxy timeouts do not mitigate it. The attacker controls only the URL string and needs no auth. ~256 KB every ~6 min (≈ 0.7 bytes/sec) keeps a server permanently unavailable. ## Impact Unauthenticated remote denial of service. One small request takes a Node service fully offline for minutes; a trickle keeps it down indefinitely. CVSS 3.1: 7.5 (High) — `AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`. ## Fix RFC 2045 type/subtype tokens never contain `/`. Excluding `/` from those two character classes removes the ambiguity and the backtracking:

const DATA_URL_PATTERN = /^([^,;/]+\/[^,;/]+)?((?:;[^,;=]+=[^,;]+)*)(;base64)?,([\s\S]*)$/;

Worst-case parse drops from ~2600 ms to ~0.002 ms. All valid `data:` URLs, including slashes in the body, parse identically.

Severity

8.2 (High)


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

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JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "axios"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.16.1"
            },
            {
              "fixed": "1.20.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-101903"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-30T15:03:21Z",
    "nvd_published_at": "2026-09-28T18:17:18Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\nAxios for Node.js parses `data:` URLs in `lib/helpers/fromDataURI.js`. The current RFC-2397 parser uses a regular expression whose media type groups allow `/` inside both sides of the `type/subtype` match. A malformed `data:` URL containing many slashes and no comma forces the JavaScript regex engine to try many possible placements for the separator before failing.\n\nApplications are affected when they pass untrusted URL strings to axios and do not reject or constrain `data:` URLs before axios parses them.\n\n## Impact\n\nAn attacker can make the Node.js event loop spend significant synchronous CPU time parsing a single malformed URL. In a server that accepts a URL from an HTTP request and calls `axios.get(url)`, this can block unrelated requests and health checks until parsing completes.\n\nThe issue is availability-only. It does not disclose data or modify requests.\n\n## Affected Functionality\n\nAffected:\n\n- Node.js HTTP adapter data URL handling.\n- `axios.get()` or equivalent calls where `config.url` has the `data:` protocol.\n\nNot affected:\n\n- Browser fetch/XHR URL handling.\n- Node requests where the application rejects `data:` URLs before calling axios.\n- Older checked `0.x` data URL parser shape unless separately proven vulnerable.\n\n## Technical Details\n\n`lib/helpers/fromDataURI.js` contains:\n\n```js\nconst DATA_URL_PATTERN = /^([^,;]+\\/[^,;]+)?((?:;[^,;=]+=[^,;]+)*)(;base64)?,([\\s\\S]*)$/;\n```\n\nThe `[^,;]+` groups include `/`, so a long string of slashes without a comma can be partitioned around the required `\\/` in many ways before the match fails. The match runs before axios can apply request timeout behavior, so `timeout` does not mitigate the parsing pause.\n\nLocal timing on axios `1.18.1` with small payloads showed about 2.4 ms at 1000 slashes, 16.6 ms at 3000 slashes, and 71.5 ms at 6000 slashes, consistent with the submitted quadratic scaling while avoiding long-running payloads.\n\n## Proof of Concept of Attack\n\nConstrained helper-level demonstration:\n\n```js\nimport axios from \u0027axios\u0027;\n\nawait axios.get(\u0027data:\u0027 + \u0027/\u0027.repeat(6000));\n```\n\nThe request fails after parsing, but the failure is delayed by synchronous regex work. Larger payloads increase the pause substantially.\n\n## Workarounds\n\nReject `data:` URLs before passing untrusted input to axios, or enforce a strict maximum URL length for URL-fetching endpoints. Applications that do not need `data:` URL support should deny that protocol explicitly.\n\n\u003cdetails\u003e\n  \u003csummary\u003e\u003ch3\u003eOriginal report\u003c/h3\u003e\u003c/summary\u003e\n  \n# ReDoS in `fromDataURI` data: URL parser freezes the event loop (DoS)\n\n## Affected\n- Package: `axios` (Node.js http adapter)\n- Versions: 1.x (regex present on `v1.x`, current release line)\n- File: `lib/helpers/fromDataURI.js`\n- CWE-1333 (Inefficient Regular Expression Complexity)\n\n## Issue\n`fromDataURI` parses `data:` URLs with this regex:\n\n```js\n// lib/helpers/fromDataURI.js:9\nconst DATA_URL_PATTERN = /^([^,;]+\\/[^,;]+)?((?:;[^,;=]+=[^,;]+)*)(;base64)?,([\\s\\S]*)$/;\n```\n\nThe mediatype tokens `[^,;]+` include `/`, so they can span multiple slashes ambiguously. A `data:` URL made of many slashes with no comma forces the engine to try every way to place the single `\\/` divider before failing \u2014 quadratic O(n\u00b2) backtracking. It runs synchronously on the main thread, so the whole Node event loop is frozen for the entire parse. Reachable through the public API on the Node http adapter (`axios.get(url)`); the browser fetch/xhr adapters are not affected because they do not call `fromDataURI`.\n\nA configured `timeout` does not help: the freeze happens during parsing, before any network timer can fire.\n\n## PoC (minimal)\n```js\nimport axios from \u0027axios\u0027;\n// ~256 KB data: URL of pure slashes, no comma\nawait axios.get(\u0027data:\u0027 + \u0027/\u0027.repeat(262139)); // blocks the event loop ~6 min, then throws\n```\n\n## Lab results\nSingle-threaded \"fetch a user-supplied URL\" service (link-preview style) calling `axios.get` on a JSON body `{ \"url\": \"...\" }`, with `timeout: 1000` set.\n\nScaling is clean O(n\u00b2) (constant k \u2248 5.6e-6 ms/byte\u00b2, stable across sizes):\n\n| data: URL size | Event-loop freeze (one request) |\n| --- | --- |\n| 32 KB | 6.3 s (measured end-to-end; server logged `event loop BLOCKED for 6.30s`) |\n| 64 KB | ~24 s |\n| 128 KB | ~96 s |\n| 256 KB | ~385 s (~6.4 min) |\n| 1 MB | ~100 min |\n\nDuring the freeze the server answers nothing: a `/healthz` liveness probe times out for the whole window, and the server\u0027s own event-loop monitor cannot even log until the parse finishes. In a run through an intercepting proxy, the proxy hit its 120 s upstream timeout and gave up, while the origin stayed pegged at 100% CPU on one core past that \u2014 client/proxy timeouts do not mitigate it.\n\nThe attacker controls only the URL string and needs no auth. ~256 KB every ~6 min (\u2248 0.7 bytes/sec) keeps a server permanently unavailable.\n\n## Impact\nUnauthenticated remote denial of service. One small request takes a Node service fully offline for minutes; a trickle keeps it down indefinitely.\nCVSS 3.1: 7.5 (High) \u2014 `AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`.\n\n## Fix\nRFC 2045 type/subtype tokens never contain `/`. Excluding `/` from those two character classes removes the ambiguity and the backtracking:\n\n```js\nconst DATA_URL_PATTERN = /^([^,;/]+\\/[^,;/]+)?((?:;[^,;=]+=[^,;]+)*)(;base64)?,([\\s\\S]*)$/;\n```\n\nWorst-case parse drops from ~2600 ms to ~0.002 ms. All valid `data:` URLs, including slashes in the body, parse identically.\n\u003c/details\u003e\n\n---",
  "id": "GHSA-c29m-xwm3-cm6r",
  "modified": "2026-09-30T15:03:22Z",
  "published": "2026-09-30T15:03:21Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/security/advisories/GHSA-c29m-xwm3-cm6r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-101903"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/pull/11141"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/commit/d19040bda7a8be2f82c3c6e1a5bc03917daee39a"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/axios/axios"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/releases/tag/v1.20.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Axios: ReDoS in fromDataURI data: URL parser freezes the Node event loop (DoS)"
}

CVE-2026-101903 (GCVE-0-2026-101903)

Vulnerability from cvelistv5 – Published: 2026-09-28 17:25 – Updated: 2026-09-28 17:49

Title

Axios: ReDoS in fromDataURI data: URL parser freezes the Node event loop (DoS)

Summary

Axios is a promise-based HTTP client for the browser and Node.js. From 1.16.1 until 1.20.0, the RFC 2397 regular expression allows slash characters on both sides of the media-type separator. An application passes an attacker-controlled malformed data URL containing many slash characters and no comma. the JavaScript regular-expression engine explores many separator placements before rejecting the URL. Synchronous excessive backtracking can block the Node.js event loop and cause denial of service. The affected identifiers are fromDataURI, DATA_URL_PATTERN, data:. This issue is fixed in version 1.20.0.

Severity

8.2 (High)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-28 17:48 UTC

CWE

CWE-1333 - Inefficient Regular Expression Complexity

Assigner

GitHub_M mitre root Scorecard

References

4 references

URL	Tags
https://github.com/axios/axios/security/advisorie…	x_refsource_CONFIRM
https://github.com/axios/axios/pull/11141	x_refsource_MISC
https://github.com/axios/axios/commit/d19040bda7a…	x_refsource_MISC
https://github.com/axios/axios/releases/tag/v1.20.0	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
axios	axios	Affected: >= 1.16.1, < 1.20.0

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-101903",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-28T17:48:43.428191Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-09-28T17:49:24.777Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/axios/axios/security/advisories/GHSA-c29m-xwm3-cm6r"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "axios",
          "vendor": "axios",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 1.16.1, \u003c 1.20.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Axios is a promise-based HTTP client for the browser and Node.js. From 1.16.1 until 1.20.0, the RFC 2397 regular expression allows slash characters on both sides of the media-type separator. An application passes an attacker-controlled malformed data URL containing many slash characters and no comma. the JavaScript regular-expression engine explores many separator placements before rejecting the URL. Synchronous excessive backtracking can block the Node.js event loop and cause denial of service. The affected identifiers are fromDataURI, DATA_URL_PATTERN, data:. This issue is fixed in version 1.20.0."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 8.2,
            "baseSeverity": "HIGH",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
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            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE"
          }
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      "problemTypes": [
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          "descriptions": [
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              "cweId": "CWE-1333",
              "description": "CWE-1333: Inefficient Regular Expression Complexity",
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              "type": "CWE"
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      "providerMetadata": {
        "dateUpdated": "2026-09-28T17:26:41.005Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
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          "tags": [
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        "discovery": "UNKNOWN"
      },
      "title": "Axios: ReDoS in fromDataURI data: URL parser freezes the Node event loop (DoS)"
    }
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    "dateReserved": "2026-09-28T15:55:37.907Z",
    "dateUpdated": "2026-09-28T17:49:24.777Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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Action not permitted

GHSA-C29M-XWM3-CM6R

Summary

Impact

Affected Functionality

Technical Details

Proof of Concept of Attack

Workarounds

Original report

CVE-2026-101903 (GCVE-0-2026-101903)

Tags

Sightings

Nomenclature

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