{"cve":"CVE-2026-52845","nvd":{"published":"2026-06-23T18:18:05.267","modified":"2026-10-25T23:10:00.167","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N","score":8.1},"cwes":["CWE-287","CWE-290","CWE-444"],"references":["https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g","https://access.redhat.com/security/cve/CVE-2026-52845","https://bugzilla.redhat.com/show_bug.cgi?id=2491907","https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g","https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json"],"products":["caddyserver:caddy"],"source":"nvd","synced_at":"2026-10-25T23:44:33.281319194+00:00"},"epss":{"cve":"CVE-2026-52845","score":0.00445,"percentile":0.38472,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-f59h-q822-g45g","url":"https://osv.dev/vulnerability/GHSA-f59h-q822-g45g","summary":"Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`","modified":"2026-07-24T19:11:38.174856198Z","packages":[{"ecosystem":"Go","name":"github.com/caddyserver/caddy/v2","purl":"pkg:golang/github.com/caddyserver/caddy/v2","ranges":["<2.11.4"],"fixed":["2.11.4"]},{"ecosystem":"Go","name":"github.com/caddyserver/caddy","purl":"pkg:golang/github.com/caddyserver/caddy","ranges":["<=1.0.5"],"fixed":[]}]},{"id":"GO-2026-5346","url":"https://osv.dev/vulnerability/GO-2026-5346","summary":"Caddy: FastCGI header normalization bypass in forward_auth copy_headers in github.com/caddyserver/caddy","modified":"2026-07-24T19:00:22.820653013Z","packages":[{"ecosystem":"Go","name":"github.com/caddyserver/caddy/v2","purl":"pkg:golang/github.com/caddyserver/caddy/v2","ranges":["<2.11.4"],"fixed":["2.11.4"]}]}],"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."]}