GHSA-W9J2-PVGH-6H63

Vulnerability from github – Published: 2026-05-05 00:21 – Updated: 2026-05-05 00:21
VLAI
Summary
Axios: Authentication Bypass via Prototype Pollution Gadget in `validateStatus` Merge Strategy
Details

Vulnerability Disclosure: Authentication Bypass via Prototype Pollution Gadget in validateStatus Merge Strategy

Summary

The Axios library is vulnerable to a Prototype Pollution "Gadget" attack that allows any Object.prototype pollution to silently suppress all HTTP error responses (401, 403, 500, etc.), causing them to be treated as successful responses. This completely bypasses application-level authentication and error handling.

The root cause is that validateStatus is the only config property using the mergeDirectKeys merge strategy, which uses JavaScript's in operator — an operator that inherently traverses the prototype chain. When Object.prototype.validateStatus is polluted with () => true, all HTTP status codes are accepted as success.

Severity: High (CVSS 8.2) Affected Versions: All versions (v0.x - v1.x including v1.15.0) Vulnerable Component: lib/core/mergeConfig.js (mergeDirectKeys strategy) + lib/core/settle.js

CWE

  • CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
  • CWE-287: Improper Authentication

CVSS 3.1

Score: 8.2 (High)

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

Metric Value Justification
Attack Vector Network PP is triggered remotely
Attack Complexity Low Once PP exists, a single property assignment exploits this. Consistent with GHSA-fvcv-3m26-pcqx
Privileges Required None No authentication needed
User Interaction None No user interaction required
Scope Unchanged Impact within the application
Confidentiality Low 401 treated as success may expose data behind auth gates
Integrity High All error handling and auth checks are silently bypassed — application operates on invalid assumptions
Availability None The function works correctly (returns true), no crash

Usage of "Helper" Vulnerabilities

This vulnerability requires Zero Direct User Input.

If an attacker can pollute Object.prototype via any other library in the stack, Axios will automatically inherit the polluted validateStatus function during config merge. The in operator in mergeDirectKeys makes this property uniquely susceptible to prototype pollution compared to all other config properties.

Why validateStatus Is Uniquely Vulnerable

All other config properties use defaultToConfig2, which reads config2[prop] (traverses prototype). But validateStatus uses mergeDirectKeys, which uses the in operator:

// mergeConfig.js:58-64 — mergeDirectKeys (ONLY used by validateStatus)
function mergeDirectKeys(a, b, prop) {
  if (prop in config2) {           // ← `in` traverses prototype chain!
    return getMergedValue(a, b);
  } else if (prop in config1) {
    return getMergedValue(undefined, a);
  }
}

// mergeConfig.js:94
const mergeMap = {
  // ... all others use defaultToConfig2 ...
  validateStatus: mergeDirectKeys,   // ← ONLY property using this strategy
};

The in operator is a more aggressive prototype traversal than property access. While config2['validateStatus'] also traverses the prototype, the explicit in check makes the intent clearer and the vulnerability more direct.

Proof of Concept

1. The Setup (Simulated Pollution)

Object.prototype.validateStatus = () => true;

2. The Gadget Trigger (Safe Code)

// Application checks authentication via HTTP status codes
try {
  const response = await axios.get('https://api.internal/admin/users');
  // Developer expects: 401 → catch block → redirect to login
  // Reality: 401 → treated as success → displays admin data
  processAdminData(response.data);  // Executes with 401 response body!
} catch (error) {
  redirectToLogin();  // NEVER REACHED for 401/403/500
}

3. The Execution

// mergeConfig.js:58 — 'validateStatus' in config2
// config2 = { url: '/admin/users', method: 'get' }
// 'validateStatus' in config2 → checks prototype → finds () => true → TRUE
// → getMergedValue(defaultValidator, () => true) → returns () => true

// settle.js:16 — ALL status codes resolve
const validateStatus = response.config.validateStatus;  // () => true
if (!response.status || !validateStatus || validateStatus(response.status)) {
  resolve(response);  // 401, 403, 500 all resolve here!
}

4. The Impact

Before pollution:
  HTTP 200 → resolve (success)
  HTTP 401 → reject (auth error) → redirectToLogin()
  HTTP 403 → reject (forbidden) → showAccessDenied()
  HTTP 500 → reject (server error) → showErrorPage()

After pollution:
  HTTP 200 → resolve (success)
  HTTP 401 → resolve (SUCCESS!) → processAdminData() with error body
  HTTP 403 → resolve (SUCCESS!) → application thinks user has access
  HTTP 500 → resolve (SUCCESS!) → application processes error as data

Verified PoC Output

--- Before Pollution ---
401: REJECTED as expected - Request failed with status code 401
500: REJECTED as expected - Request failed with status code 500

--- After Pollution ---
200: RESOLVED as success (status: 200)
301: RESOLVED as success (status: 301)
401: RESOLVED as success (status: 401)
403: RESOLVED as success (status: 403)
404: RESOLVED as success (status: 404)
500: RESOLVED as success (status: 500)
503: RESOLVED as success (status: 503)

--- Authentication Bypass Demo ---
Auth check bypassed! 401 treated as success.
Application proceeds with: { status: 401, message: 'Response with status 401' }

Impact Analysis

  • Authentication Bypass: Applications relying on axios rejecting 401/403 to enforce auth will silently accept unauthorized responses, allowing unauthenticated access to protected resources.
  • Silent Error Swallowing: 500-series errors are treated as success, causing applications to process error bodies as valid data — leading to data corruption or logic errors.
  • Security Control Bypass: Rate limiting (429), WAF blocks (403), and CAPTCHA challenges are suppressed.
  • Universal Scope: Affects every axios instance in the application, including third-party libraries.

Recommended Fix

Replace the in operator with hasOwnProperty in mergeDirectKeys:

// FIXED: lib/core/mergeConfig.js
function mergeDirectKeys(a, b, prop) {
  if (Object.prototype.hasOwnProperty.call(config2, prop)) {
    return getMergedValue(a, b);
  } else if (Object.prototype.hasOwnProperty.call(config1, prop)) {
    return getMergedValue(undefined, a);
  }
}

Resources

Timeline

Date Event
2026-04-15 Vulnerability discovered during source code audit
2026-04-15 PoC developed and vulnerability confirmed
2026-04-16 Report revised for accuracy
TBD Report submitted to vendor via GitHub Security Advisory
Severity
4.8 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
Show details on source website
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{
  "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-2026-42041"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1321",
      "CWE-287"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-05T00:21:39Z",
    "nvd_published_at": "2026-04-24T18:16:31Z",
    "severity": "MODERATE"
  },
  "details": "# Vulnerability Disclosure: Authentication Bypass via Prototype Pollution Gadget in `validateStatus` Merge Strategy\n\n## Summary\n\nThe Axios library is vulnerable to a Prototype Pollution \"Gadget\" attack that allows any `Object.prototype` pollution to **silently suppress all HTTP error responses** (401, 403, 500, etc.), causing them to be treated as successful responses. This completely bypasses application-level authentication and error handling.\n\nThe root cause is that `validateStatus` is the **only** config property using the `mergeDirectKeys` merge strategy, which uses JavaScript\u0027s `in` operator \u2014 an operator that inherently traverses the prototype chain. When `Object.prototype.validateStatus` is polluted with `() =\u003e true`, all HTTP status codes are accepted as success.\n\n**Severity:** High (CVSS 8.2)\n**Affected Versions:** All versions (v0.x - v1.x including v1.15.0)\n**Vulnerable Component:** `lib/core/mergeConfig.js` (`mergeDirectKeys` strategy) + `lib/core/settle.js`\n\n## CWE\n\n- **CWE-1321:** Improperly Controlled Modification of Object Prototype Attributes (\u0027Prototype Pollution\u0027)\n- **CWE-287:** Improper Authentication\n\n## CVSS 3.1\n\n**Score: 8.2 (High)**\n\nVector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N`\n\n| Metric | Value | Justification |\n|---|---|---|\n| Attack Vector | Network | PP is triggered remotely |\n| Attack Complexity | Low | Once PP exists, a single property assignment exploits this. Consistent with GHSA-fvcv-3m26-pcqx |\n| Privileges Required | None | No authentication needed |\n| User Interaction | None | No user interaction required |\n| Scope | Unchanged | Impact within the application |\n| Confidentiality | Low | 401 treated as success may expose data behind auth gates |\n| Integrity | High | All error handling and auth checks are silently bypassed \u2014 application operates on invalid assumptions |\n| Availability | None | The function works correctly (returns true), no crash |\n\n## Usage of \"Helper\" Vulnerabilities\n\nThis vulnerability requires **Zero Direct User Input**.\n\nIf an attacker can pollute `Object.prototype` via any other library in the stack, Axios will automatically inherit the polluted `validateStatus` function during config merge. The `in` operator in `mergeDirectKeys` makes this property **uniquely susceptible** to prototype pollution compared to all other config properties.\n\n## Why `validateStatus` Is Uniquely Vulnerable\n\nAll other config properties use `defaultToConfig2`, which reads `config2[prop]` (traverses prototype). But `validateStatus` uses `mergeDirectKeys`, which uses the `in` operator:\n\n```javascript\n// mergeConfig.js:58-64 \u2014 mergeDirectKeys (ONLY used by validateStatus)\nfunction mergeDirectKeys(a, b, prop) {\n  if (prop in config2) {           // \u2190 `in` traverses prototype chain!\n    return getMergedValue(a, b);\n  } else if (prop in config1) {\n    return getMergedValue(undefined, a);\n  }\n}\n\n// mergeConfig.js:94\nconst mergeMap = {\n  // ... all others use defaultToConfig2 ...\n  validateStatus: mergeDirectKeys,   // \u2190 ONLY property using this strategy\n};\n```\n\nThe `in` operator is a **more aggressive** prototype traversal than property access. While `config2[\u0027validateStatus\u0027]` also traverses the prototype, the explicit `in` check makes the intent clearer and the vulnerability more direct.\n\n## Proof of Concept\n\n### 1. The Setup (Simulated Pollution)\n\n```javascript\nObject.prototype.validateStatus = () =\u003e true;\n```\n\n### 2. The Gadget Trigger (Safe Code)\n\n```javascript\n// Application checks authentication via HTTP status codes\ntry {\n  const response = await axios.get(\u0027https://api.internal/admin/users\u0027);\n  // Developer expects: 401 \u2192 catch block \u2192 redirect to login\n  // Reality: 401 \u2192 treated as success \u2192 displays admin data\n  processAdminData(response.data);  // Executes with 401 response body!\n} catch (error) {\n  redirectToLogin();  // NEVER REACHED for 401/403/500\n}\n```\n\n### 3. The Execution\n\n```javascript\n// mergeConfig.js:58 \u2014 \u0027validateStatus\u0027 in config2\n// config2 = { url: \u0027/admin/users\u0027, method: \u0027get\u0027 }\n// \u0027validateStatus\u0027 in config2 \u2192 checks prototype \u2192 finds () =\u003e true \u2192 TRUE\n// \u2192 getMergedValue(defaultValidator, () =\u003e true) \u2192 returns () =\u003e true\n\n// settle.js:16 \u2014 ALL status codes resolve\nconst validateStatus = response.config.validateStatus;  // () =\u003e true\nif (!response.status || !validateStatus || validateStatus(response.status)) {\n  resolve(response);  // 401, 403, 500 all resolve here!\n}\n```\n\n### 4. The Impact\n\n```\nBefore pollution:\n  HTTP 200 \u2192 resolve (success)\n  HTTP 401 \u2192 reject (auth error) \u2192 redirectToLogin()\n  HTTP 403 \u2192 reject (forbidden) \u2192 showAccessDenied()\n  HTTP 500 \u2192 reject (server error) \u2192 showErrorPage()\n\nAfter pollution:\n  HTTP 200 \u2192 resolve (success)\n  HTTP 401 \u2192 resolve (SUCCESS!) \u2192 processAdminData() with error body\n  HTTP 403 \u2192 resolve (SUCCESS!) \u2192 application thinks user has access\n  HTTP 500 \u2192 resolve (SUCCESS!) \u2192 application processes error as data\n```\n\n## Verified PoC Output\n\n```\n--- Before Pollution ---\n401: REJECTED as expected - Request failed with status code 401\n500: REJECTED as expected - Request failed with status code 500\n\n--- After Pollution ---\n200: RESOLVED as success (status: 200)\n301: RESOLVED as success (status: 301)\n401: RESOLVED as success (status: 401)\n403: RESOLVED as success (status: 403)\n404: RESOLVED as success (status: 404)\n500: RESOLVED as success (status: 500)\n503: RESOLVED as success (status: 503)\n\n--- Authentication Bypass Demo ---\nAuth check bypassed! 401 treated as success.\nApplication proceeds with: { status: 401, message: \u0027Response with status 401\u0027 }\n```\n\n## Impact Analysis\n\n- **Authentication Bypass:** Applications relying on axios rejecting 401/403 to enforce auth will silently accept unauthorized responses, allowing unauthenticated access to protected resources.\n- **Silent Error Swallowing:** 500-series errors are treated as success, causing applications to process error bodies as valid data \u2014 leading to data corruption or logic errors.\n- **Security Control Bypass:** Rate limiting (429), WAF blocks (403), and CAPTCHA challenges are suppressed.\n- **Universal Scope:** Affects every axios instance in the application, including third-party libraries.\n\n## Recommended Fix\n\nReplace the `in` operator with `hasOwnProperty` in `mergeDirectKeys`:\n\n```javascript\n// FIXED: lib/core/mergeConfig.js\nfunction mergeDirectKeys(a, b, prop) {\n  if (Object.prototype.hasOwnProperty.call(config2, prop)) {\n    return getMergedValue(a, b);\n  } else if (Object.prototype.hasOwnProperty.call(config1, prop)) {\n    return getMergedValue(undefined, a);\n  }\n}\n```\n\n## Resources\n\n- [CWE-1321: Prototype Pollution](https://cwe.mitre.org/data/definitions/1321.html)\n- [CWE-287: Improper Authentication](https://cwe.mitre.org/data/definitions/287.html)\n- [GHSA-fvcv-3m26-pcqx: Related PP Gadget in Axios](https://github.com/advisories/GHSA-fvcv-3m26-pcqx)\n- [MDN: `in` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in)\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| 2026-04-15 | PoC developed and vulnerability confirmed |\n| 2026-04-16 | Report revised for accuracy |\n| TBD | Report submitted to vendor via GitHub Security Advisory |",
  "id": "GHSA-w9j2-pvgh-6h63",
  "modified": "2026-05-05T00:21:40Z",
  "published": "2026-05-05T00:21:39Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/security/advisories/GHSA-w9j2-pvgh-6h63"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42041"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/axios/axios"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Axios: Authentication Bypass via Prototype Pollution Gadget in `validateStatus` Merge Strategy"
}


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