CVE-2026-85720: AsyncHttpClient: Origin credentials sent to the proxy on the plaintext CONNECT request
Impact When a request uses an HTTP proxy to reach an HTTPS origin, the client opens the tunnel with a plaintext CONNECT sent to the proxy before any TLS exists. On affected versions the origin's preemptive credentials were added to that CONNECT. A Basic realm sent Authorization: Basic base64(user:pass) to the proxy in the clear, and NTLM, SPNEGO or Kerberos realms sent their token. The proxy, and anyone who can read the client to proxy hop, saw credentials that were meant only for the origin.
Affected versions 3.x: up to and including 3.0.11 2.x: up to and including 2.16.0
Patches Fixed in 3.0.12 on the 3.x line and in 2.16.1 on the 2.x line. The origin Basic or Digest Authorization is no longer put on the CONNECT; it is added to the tunnelled request once the tunnel is up. The per-connection NTLM, Kerberos and SPNEGO token is likewise no longer attached on the tunnel path; it never reached the origin there in any case, and the challenge flow still negotiates it inside the tunnel.
Workarounds Do not use preemptive origin authentication together with an HTTP proxy, or reach the origin without a CONNECT proxy.
Details NettyRequestFactory added the origin Authorization to every request it built, including the CONNECT, and NettyRequestSender did the same for the per-connection NTLM or SPNEGO token in sendRequestWithNewChannel. Both now skip the CONNECT.
Note that 3.0.12 is itself affected by a separate issue, GHSA-rqf5-2wxv-rjf4, where a Digest challenge the client cannot read downgrades to Basic and sends the password in cleartext. Upgrade to 3.0.13 to pick up both fixes.
Other sources
The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP requests and asynchronously process HTTP responses. From 2.0.0 until 2.16.1 and 3.0.12, a request using an HTTP proxy to reach an HTTPS origin can expose preemptive origin credentials because NettyRequestFactory and NettyRequestSender.sendRequestWithNewChannel attach Authorization to the plaintext CONNECT request before the TLS tunnel exists. Basic or Digest credentials and per-connection NTLM, Kerberos, or SPNEGO tokens intended for the origin are therefore visible to the proxy and to observers on the client-to-proxy hop. The tunneled request still receives origin Authorization after the tunnel is established, while Proxy-Authorization remains on CONNECT for its intended proxy recipient. This issue is fixed in versions 2.16.1 and 3.0.12.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
maven/org.asynchttpclient:async-http-clientto a version that resolves this vulnerability.Fixed in 2.16.1 - Upgrade
Upgrade
maven/org.asynchttpclient:async-http-clientto a version that resolves this vulnerability.Fixed in 3.0.12 - Upgrade
Upgrade
AsyncHttpClientto a version that resolves this vulnerability.Fixed in 2.16.1 - Upgrade
Upgrade
AsyncHttpClientto a version that resolves this vulnerability.Fixed in 3.0.12 - Upgrade
Upgrade
AsyncHttpClientto a version that resolves this vulnerability.Fixed in 3.0.13 - Compensating control
Do not use preemptive origin authentication together with an HTTP proxy, or reach the origin without a CONNECT proxy.
Event History
Frequently Asked Questions
Which deployments are exposed to credential disclosure?
Java applications using AsyncHttpClient versions from 2.0.0 until 2.16.1 or 3.0.12 are exposed when they use an HTTP proxy to access an HTTPS origin and send preemptive origin credentials.
What credentials can be disclosed, and who can see them?
Basic or Digest origin credentials, plus per-connection NTLM, Kerberos, or SPNEGO tokens, can be attached to the plaintext CONNECT request. They are visible to the HTTP proxy and to observers on the client-to-proxy network hop.
Does proxy authentication cause the issue?
No. Proxy-Authorization remains on CONNECT for the proxy as intended; the issue is that origin Authorization is also sent before the TLS tunnel is established.
What is the immediate remediation?
Upgrade AsyncHttpClient to version 2.16.1 or 3.0.12. If upgrading cannot happen immediately, avoid using an HTTP proxy for HTTPS requests that use preemptive origin credentials.