{"id":"CVE-2026-52845","aliases":["GHSA-f59h-q822-g45g","GO-2026-5346"],"url":"https://o3.security/vulnerability/CVE-2026-52845","summary":"Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`","details":"Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the exact client-supplied identity header before copying the trusted value from the auth gateway. But when the request later goes through php_fastcgi, Caddy normalizes HTTP headers into CGI variables by replacing - with _. This lets a client send an underscore alias that survives the forward_auth delete step but becomes the same PHP/FastCGI variable. Result: a remote client can inject or sometimes override identity/group headers trusted by PHP/FastCGI applications behind Caddy. This vulnerability is fixed in 2.11.4.","published":"2026-06-23T17:52:01.871Z","modified":"2026-07-24T19:11:38.174856198Z","cvss":{"score":8.1,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N"},"epss":{"score":0.00297,"percentile":0.22019,"asOf":"2026-08-10"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/caddyserver/caddy/v2","fixedVersion":"2.11.4"},{"ecosystem":"Go","name":"github.com/caddyserver/caddy","fixedVersion":null}],"fix":null,"references":[{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-52845"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52845.json"},{"type":"ADVISORY","url":"https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-52845"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2491907"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-24T19:11:38.174856198Z"}}