As a result, subsequent connection pool operations, tunneling requests, and realm-based authentication processes use stale request data. This leads to the application sending sensitive headers, such as Authorization, to the wrong host. Furthermore, if the protocol upgrades from HTTP to HTTPS during the replay, the client may fail to install an SSL handler, causing the transmission of credentials in cleartext. Defenders should note that this behavior occurs via documented features, making it a design-level defect rather than a recent regression.

Attack Chain

1. An application configured with AsyncHttpClient attempts to perform a failover or retry operation upon encountering an error.
2. The ResponseFilter or IOException retry path triggers a request replay to a new destination host (Host B).
3. The NettyRequestSender component initiates the request but fails to update the target request object, retaining the original destination (Host A) headers and metadata.
4. The client's connection pool incorrectly keys the connection to Host B under the identity of Host A.
5. Subsequent authentication routines read the stale target request, attaching Host A's Authorization header to the traffic destined for Host B.
6. The NettyConnectListener logic fails to install an SSL handler if the original request was HTTP and the replay is HTTPS, bypassing intended security controls.
7. The replayed request - containing sensitive data - is transmitted to Host B, resulting in unauthorized credential exposure.

Impact

The vulnerability results in the unauthorized exposure of authentication credentials and potentially sensitive request content to third-party or unauthorized hosts. This impact is significant for applications that utilize connection pooling, automated failover, or retry mechanisms in environments requiring strict confidentiality. Any service integrated with this library in these versions is susceptible to credential harvesting if an adversary controls or can intercept the replayed destination.

Recommendation

• Upgrade to version 3.0.13 or 2.16.1 of async-http-client immediately to patch the target request management logic.
• If upgrading is not immediately possible, disable ResponseFilter logic that redirects requests to different hosts.
• Disable automatic request retries for applications configured with credentials or that operate via proxies to mitigate the risk of accidental credential leakage during failover scenarios.