{"id":"CVE-2026-27586","aliases":["GHSA-hffm-g8v7-wrv7","GO-2026-4539"],"url":"https://o3.security/vulnerability/CVE-2026-27586","summary":"Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed","details":"Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, two swallowed errors in `ClientAuthentication.provision()` cause mTLS client certificate authentication to silently fail open when a CA certificate file is missing, unreadable, or malformed. The server starts without error but accepts any client certificate signed by any system-trusted CA, completely bypassing the intended private CA trust boundary. Any deployment using `trusted_ca_cert_file` or `trusted_ca_certs_pem_files` for mTLS will silently degrade to accepting any system-trusted client certificate if the CA file becomes unavailable. This can happen due to a typo in the path, file rotation, corruption, or permission changes. The server gives no indication that mTLS is misconfigured. Version 2.11.1 fixes the vulnerability.","published":"2026-02-24T16:08:20.569Z","modified":"2026-08-12T03:51:29.760870785Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/caddyserver/caddy/v2","fixedVersion":"2.11.1"}],"fix":null,"references":[{"type":"WEB","url":"https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48"},{"type":"WEB","url":"https://github.com/caddyserver/caddy/releases/tag/v2.11.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27586.json"},{"type":"ADVISORY","url":"https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-27586"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:29.760870785Z"}}