CVE-2026-56866

Name	CVE-2026-56866
Description	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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
golang-1.19 (PTS)	bookworm	1.19.8-2	vulnerable
golang-1.24 (PTS)	trixie	1.24.4-1	vulnerable
golang-1.26 (PTS)	forky, sid	1.26.10-1	fixed
golang-1.27 (PTS)	forky, sid	1.27.3-1	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version
golang-1.19	source	(unstable)	(unfixed)
golang-1.24	source	(unstable)	(unfixed)
golang-1.25	source	(unstable)	(unfixed)
golang-1.26	source	(unstable)	1.26.9-1
golang-1.27	source	(unstable)	1.27.2-1

Notes

[trixie] - golang-1.24 <no-dsa> (Minor issue)
[bookworm] - golang-1.19 <postponed> (Minor issue)
https://www.openwall.com/lists/oss-security/2026/10/08/9
https://github.com/golang/go/issues/81740
Fixed by: https://github.com/golang/go/commit/76875df0f3425f69e4dc2c439040a248b6107854 (go1.27.2)
Fixed by: https://github.com/golang/go/commit/3fe1aac0ce941cb16b0ec5d489827cf1c58197c4 (go1.26.9)