{"id":"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.","aliases":["GHSA-f59h-q822-g45g"],"modified":"2026-07-08T08:10:42.716952552Z","published":"2026-06-23T17:52:01.871Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52845.json","cwe_ids":["CWE-287","CWE-290","CWE-444"],"cna_assigner":"GitHub_M"},"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"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/caddyserver/caddy","events":[{"introduced":"0"},{"fixed":"e2eee6a7fce366321294c9c2a79f3146891dcbdf"}],"database_specific":{"cpe":"cpe:2.3:a:caddyserver:caddy:*:*:*:*:*:*:*:*","source":["AFFECTED_FIELD","CPE_RANGE"],"extracted_events":[{"introduced":"0"},{"fixed":"2.11.4"}]}}],"versions":["v2.11.3","v2.11.2","v2.11.1","v2.11.0","v2.11.0-beta.2","v2.11.0-beta.1","v2.10.2","v2.10.1","v2.10.0","v2.10.0-beta.4","v2.10.0-beta.3","v2.9.1","v2.10.0-beta.2","v2.10.0-beta.1","v2.9.0","v2.9.0-beta.3","v2.9.0-beta.2","v2.9.0-beta.1","v2.8.4","v2.8.3","v2.8.2","v2.8.1","v2.8.0","v2.8.0-rc.1","v2.8.0-beta.2","v2.8.0-beta.1","v2.7.5","v2.7.4","v2.7.3","v2.7.2","v2.7.1","v2.7.0","v2.7.0-beta.2","v2.7.0-beta.1","v2.6.4","v2.6.3","v2.6.2","v2.6.1","v2.6.0","v2.6.0-beta.5","v2.6.0-beta.4","v2.6.0-beta.3","v2.6.0-beta.2","v2.6.0-beta.1","v2.5.2","v2.5.1","v2.5.0","v2.5.0-rc.1","v2.5.0-beta.1","v2.4.6","v2.4.5","v2.4.4","v2.4.3","v2.4.2","v2.4.1","v2.4.0","v2.4.0-rc.1","v2.4.0-beta.2","v2.4.0-beta.1","v2.3.0-rc.2","v2.3.0","v2.3.0-rc.1","v2.3.0-beta.1","v2.2.3","v2.2.1","v2.2.0","v2.2.0-rc.3","v2.2.0-rc.2","v2.2.0-rc.1","v2.1.1","v2.1.0","v2.1.0-beta.2","v2.1.0-beta.1","v2.0.0","v2.0.0-rc.3","v2.0.0-rc.2","v2.0.0-rc.1","v2.0.0-beta.20","v2.0.0-beta.19","v2.0.0-beta.18","v2.0.0-beta.17","v2.0.0-beta.16","v2.0.0-beta.15","v2.0.0-beta.14","v2.0.0-beta.13","v2.0.0-beta12","v2.0.0-beta11","v2.0.0-beta10","v2.0.0-beta9","v2.0.0-beta8","v2.0.0-beta7","v2.0.0-beta6","v2.0.0-beta5","v2.0.0-beta4","v2.0.0-beta3","v2.0.0-beta2","v2.0.0-beta1"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52845.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N"}]}