{"id":"CVE-2026-52845","state":"PUBLISHED","title":"Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`","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.","publishedAt":"2026-06-23T17:52:01.871Z","updatedAt":"2026-07-15T00:46:09.498Z","severity":{"score":8.1,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["caddyserver caddy"],"affected":[{"vendor":"caddyserver","product":"caddy","versions":[{"version":"< 2.11.4","status":"affected"}]}],"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://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json"],"weaknesses":["CWE-287","CWE-290","CWE-444"],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/52xxx/CVE-2026-52845.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-52845","state":"PUBLISHED","datePublished":"2026-06-23T17:52:01.871Z","dateUpdated":"2026-07-15T00:46:09.498Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-06-08T18:41:27.724Z"},"containers":{"cna":{"title":"Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"caddyserver","product":"caddy","versions":[{"version":"< 2.11.4","status":"affected"}]}],"references":[{"url":"https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g","name":"https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g","tags":["x_refsource_CONFIRM"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":8.1,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"LOW","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-287","lang":"en","description":"CWE-287: Improper Authentication","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-290","lang":"en","description":"CWE-290: Authentication Bypass by Spoofing","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-444","lang":"en","description":"CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-06-23T17:52:01.871Z"},"source":{"advisory":"GHSA-f59h-q822-g45g","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-06-24T14:25:18.472130Z","id":"CVE-2026-52845","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-06-24T14:26:28.296Z"}},{"title":"github.com/caddyserver/caddy: Caddy: Remote client can inject or override identity headers via header normalization","descriptions":[{"lang":"en","value":"A flaw was found in Caddy, an extensible server platform. A remote attacker can exploit a vulnerability in the `forward_auth` `copy_headers` functionality. This occurs because Caddy normalizes HTTP headers into Common Gateway Interface (CGI) variables by replacing hyphens with underscores, allowing a client to send an underscore alias that bypasses the header deletion step. This enables the remote attacker to inject or override identity and group headers trusted by PHP/FastCGI applications operating behind Caddy."}],"affected":[{"vendor":"Red Hat","product":"Red Hat Hardened Images","packageName":"caddy","defaultStatus":"unaffected","collectionURL":"https://access.redhat.com/downloads/content/package-browser/","cpes":["cpe:/a:redhat:hummingbird:1"]}],"references":[{"url":"https://access.redhat.com/security/cve/CVE-2026-52845","tags":["vdb-entry","x_refsource_REDHAT"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2491907","name":"RHBZ#2491907","tags":["issue-tracking","x_refsource_REDHAT"]},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json","tags":["x_sadp-csaf-vex"]}],"metrics":[{"other":{"content":{"namespace":"https://access.redhat.com/security/updates/classification/","value":"Important"},"type":"Red Hat severity rating"}},{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":8.1,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"LOW","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N","version":"3.1"},"format":"CVSS"}],"problemTypes":[{"descriptions":[{"cweId":"CWE-444","description":"Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"redhat-SADP","orgId":"0b0ca135-0b70-47e7-9f44-1890c2a1c46c","dateUpdated":"2026-07-15T00:46:09.498Z"},"datePublic":"2026-06-23T17:52:01.871Z","timeline":[{"lang":"en","time":"2026-06-23T19:02:21.968Z","value":"Reported to Red Hat."},{"lang":"en","time":"2026-06-23T17:52:01.871Z","value":"Made public."}],"x_adpType":"supplier","x_generator":{"engine":"sadp-cli 1.0.0"}}]}}}