{"id":"CVE-2026-56866","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-56866","generatedAt":"2026-10-28T02:22:13.486Z","title":"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…","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.","published":"2026-10-08T23:17:02.000Z","lastModified":"2026-10-09T16:35:36.000Z","status":"Awaiting Analysis","sourceIdentifier":"security@golang.org","cvss":{"version":"3.1","score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"},"cwe":["CWE-444"],"affected":[],"epss":{"score":0.00473,"percentile":0.40684,"date":"2026-10-26","history":[{"date":"2026-10-09","score":0.00166,"percentile":0.05313}]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.47%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[{"kind":"scored","label":"Newly scored","at":"2026-10-09T17:00:08.000Z","detail":{"from":null,"score":"7.5","severity":"HIGH","fromSeverity":null},"summary":"Now scored CVSS 7.5 HIGH."},{"kind":"new","label":"New CVE","at":"2026-10-08T23:17:02.000Z","detail":{"score":null,"severity":null,"publishedAt":"2026-10-08T23:17:01.620Z"},"summary":"New CVE, high severity (CVSS 7.5)."}],"references":[{"url":"https://go.dev/cl/847306","source":"security@golang.org"},{"url":"https://go.dev/issue/81740","source":"security@golang.org"},{"url":"https://groups.google.com/g/golang-announce/c/U2fTuyDJznI","source":"security@golang.org"},{"url":"https://pkg.go.dev/vuln/GO-2026-6605","source":"security@golang.org"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-56866","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}