CVE-2026-56866

The record

When http.Transport sends an HTTP/1 CONNECT request with a non-empty Request.Body, it writes the body directly to the connection without framing after the request headers. If the server rejects the CONNECT request with a non-2xx keep-alive response, Transport returns the connection to the idle pool. Because CONNECT requests do not have a request body, the server may interpret the trailing body bytes as a subsequent pipelined HTTP/1.1 request on the connection, leaving the pooled connection desynchronized and causing the next caller that reuses it to read the response to the injected request. In reverse proxies (including httputil.ReverseProxy) that forward CONNECT requests through a shared Transport, this can lead to cross-user response poisoning.

Affected packages

Related vulnerabilities

• CVE-2026-112212 GitLab has remediated an issue in GitLab CE/EE affecting all versions from 18.3 before… CWE-444
• CVE-2026-111750 AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. CWE-444
• CVE-2026-88829 A flaw was found in BusyBox httpd's reverse proxy feature. CWE-444
• CVE-2026-94439 When an HTTP server handler sends a 2xx response to an HTTP/1 CONNECT request and returns… CWE-444
• CVE-2026-78660 Historically, we have been rather lax about malformed framing-related headers in our… CWE-444
• CVE-2026-85078 Sanic is an opensource python web server/framework. CWE-444
• CVE-2026-81356 Inconsistent interpretation of http requests ('http request/response smuggling') in… CWE-444
• CVE-2026-19203 A client may issue specially crafted HTTP/1.1 chunked requests to a Jetty server that… CWE-444