AsyncHttpClient leaks authorization credentials to untrusted domains on cross-origin redirects

Impact

When redirect following is enabled (followRedirect(true)), AsyncHttpClient forwards Authorization and Proxy-Authorization headers along with Realm credentials to arbitrary redirect targets regardless of domain, scheme, or port changes. This leaks credentials on cross-domain redirects and HTTPS-to-HTTP downgrades.

Additionally, even when stripAuthorizationOnRedirect is set to true, the Realm object containing plaintext credentials is still propagated to the redirect request, causing credential re-generation for Basic and Digest authentication schemes via NettyRequestFactory.

An attacker who controls a redirect target (via open redirect, DNS rebinding, or MITM on HTTP) can capture Bearer tokens, Basic auth credentials, or any other Authorization header value.

Patches

Fixed in version 3.0.9 or 2.14.5. Users should upgrade immediately.

The fix automatically strips Authorization and Proxy-Authorization headers and clears Realm credentials whenever a redirect crosses origin boundaries (different scheme, host, or port) or downgrades from HTTPS to HTTP.

Workarounds

For users unable to upgrade, set (stripAuthorizationOnRedirect(true)) in the client config and avoid using Realm-based authentication with redirect following enabled. Note that (stripAuthorizationOnRedirect(true)) alone is insufficient on versions prior to 3.0.9 or 2.14.5 because the Realm bypass still re-generates credentials.

Alternatively, disable redirect following (followRedirect(false)) and handle redirects manually with origin validation.

References

• Fix commit: https://github.com/AsyncHttpClient/async-http-client/commit/6b2fbb7f8