{"cve":"CVE-2026-56866","nvd":{"published":"2026-10-08T23:17:01.620","modified":"2026-10-09T16:35:35.900","status":"Awaiting Analysis","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","score":7.5},"cwes":["CWE-444"],"references":["https://go.dev/cl/847306","https://go.dev/issue/81740","https://groups.google.com/g/golang-announce/c/U2fTuyDJznI","https://pkg.go.dev/vuln/GO-2026-6605"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:58:01.639778232+00:00"},"epss":{"cve":"CVE-2026-56866","score":0.00473,"percentile":0.40665,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GO-2026-6605","url":"https://osv.dev/vulnerability/GO-2026-6605","summary":"HTTP/1 client connection desynchronization after CONNECT rejection in net/http","modified":"2026-10-16T09:55:59.367370212Z","packages":[{"ecosystem":"Go","name":"stdlib","purl":"pkg:golang/stdlib","ranges":["<1.26.9",">=1.27.0-0 <1.27.2"],"fixed":["1.26.9","1.27.2"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}