CVE-2026-67314

axios versions >=1.15.2 and <1.18.0 contain prototype-pollution read-side gadgets in Basic auth subfield handling (lib/adapters/http.js and lib/helpers/resolveConfig.js). When an application is already affected by a separate prototype-pollution primitive and makes an axios request with an own auth object that omits the username and/or password properties, axios reads the inherited Object.prototype.username and Object.prototype.password values and uses them to construct an outbound 'Authorization: Basic ...' header. axios itself does not pollute prototypes. The practical impact is outbound request tampering: an attacker who controls the polluted prototype values can inject attacker-chosen Basic auth credentials or replace an existing Authorization header. Credential disclosure is only possible under additional application-specific conditions.

axios versions >=1.15.2 and <1.18.0 contain prototype-pollution read-side gadgets in Basic auth subfield handling (lib/adapters/http.js and lib/helpers/resolveConfig.js). When an application is already affected by a separate prototype-pollution primitive and makes an axios request with an own auth object that omits the username and/or password properties, axios reads the inherited Object.prototype.username and Object.prototype.password values and uses them to construct an outbound 'Authorization: Basic ...' header. axios itself does not pollute prototypes. The practical impact is outbound request tampering: an attacker who controls the polluted prototype values can inject attacker-chosen Basic auth credentials or replace an existing Authorization header. Credential disclosure is only possible under additional application-specific conditions.

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-xj6q-8x83-jv6g. This link is maintained to preserve external references.

Original Description

axios versions >=1.15.2 and <1.18.0 contain prototype-pollution read-side gadgets in Basic auth subfield handling (lib/adapters/http.js and lib/helpers/resolveConfig.js). When an application is already affected by a separate prototype-pollution primitive and makes an axios request with an own auth object that omits the username and/or password properties, axios reads the inherited Object.prototype.username and Object.prototype.password values and uses them to construct an outbound 'Authorization: Basic ...' header. axios itself does not pollute prototypes. The practical impact is outbound request tampering: an attacker who controls the polluted prototype values can inject attacker-chosen Basic auth credentials or replace an existing Authorization header. Credential disclosure is only possible under additional application-specific conditions.

Summary

Axios 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.

This 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 || {}.

Impact

An 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.

The 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.

This 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.

Affected Functionality

Affected functionality:

• Node HTTP adapter Basic auth handling in lib/adapters/http.js.
• Browser, web worker, React Native, and fetch shared resolver Basic auth handling in lib/helpers/resolveConfig.js.
• Requests where config.auth is an own object but username and/or password are absent own properties.

Unaffected or not accepted as core impact:

• Requests with no own auth object after mergeConfig().
• Requests with own auth.username and auth.password values.
• Normal axios request flow for inherited top-level params / paramsSerializer after the null-prototype mergeConfig() hardening.
• 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.

Technical Details

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.

In lib/adapters/http.js, axios correctly reads the top-level auth value through own('auth'), but then reads subfields directly:

const configAuth = own('auth');
if (configAuth) {
  const username = configAuth.username || '';
  const password = configAuth.password || '';
  auth = username + ':' + password;
}

If the caller passes auth: {} and Object.prototype.username/password are polluted, those direct subfield reads walk the prototype chain.

The same pattern exists in lib/helpers/resolveConfig.js:

if (auth) {
  headers.set(
    'Authorization',
    'Basic ' +
      btoa((auth.username || '') + ':' + (auth.password ? encodeUTF8(auth.password) : ''))
  );
}

The fix should guard username and password with utils.hasOwnProp, matching the proxy-auth pattern already used elsewhere.

Proof of Concept of Attack

Safe local PoC against published [email protected]:

const http = require('node:http');
const axios = require('axios');

Object.prototype.username = 'victim-user';
Object.prototype.password = 'victim-password-leaked';

const server = http.createServer((req, res) => {
  console.log({
    url: req.url,
    authorization: req.headers.authorization || null
  });

  res.end('{}');
  server.close(() => {
    delete Object.prototype.username;
    delete…

axios versions >=1.15.2 and <1.18.0 contain prototype-pollution read-side gadgets in Basic auth subfield handling (lib/adapters/http.js and lib/helpers/resolveConfig.js). When an application is already affected by a separate prototype-pollution primitive and makes an axios request with an own auth object that omits the username and/or password properties, axios reads the inherited Object.prototype.username and Object.prototype.password values and uses them to construct an outbound 'Authorization: Basic ...' header. axios itself does not pollute prototypes. The practical impact is outbound request tampering: an attacker who controls the polluted prototype values can inject attacker-chosen Basic auth credentials or replace an existing Authorization header. Credential disclosure is only possible under additional application-specific conditions.

axios versions >=1.15.2 and <1.18.0 contain prototype-pollution read-side gadgets in Basic auth subfield handling (lib/adapters/http.js and lib/helpers/resolveConfig.js). When an application is already affected by a separate prototype-pollution primitive and makes an axios request with an own auth object that omits the username and/or password properties, axios reads the inherited Object.prototype.username and Object.prototype.password values and uses them to construct an outbound 'Authorization: Basic ...' header. axios itself does not pollute prototypes. The practical impact is outbound request tampering: an attacker who controls the polluted prototype values can inject attacker-chosen Basic auth credentials or replace an existing Authorization header. Credential disclosure is only possible under additional application-specific conditions.