{"id":"CVE-2026-27586","state":"PUBLISHED","title":"Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed","description":"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.","publishedAt":"2026-02-24T16:08:20.569Z","updatedAt":"2026-02-26T20:56:20.526Z","severity":{"score":8.8,"label":"High","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:P","source":"GitHub_M"},"assigner":"GitHub_M","products":["caddyserver caddy"],"affected":[{"vendor":"caddyserver","product":"caddy","versions":[{"version":"< 2.11.1","status":"affected"}]}],"references":["https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7","https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48","https://github.com/caddyserver/caddy/releases/tag/v2.11.1"],"weaknesses":["CWE-755"],"ingestedAt":"2026-10-29T20:11:31.369Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/27xxx/CVE-2026-27586.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-27586","state":"PUBLISHED","datePublished":"2026-02-24T16:08:20.569Z","dateUpdated":"2026-02-26T20:56:20.526Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-02-20T17:40:28.450Z"},"containers":{"cna":{"title":"Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"caddyserver","product":"caddy","versions":[{"version":"< 2.11.1","status":"affected"}]}],"references":[{"url":"https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7","name":"https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7","tags":["x_refsource_CONFIRM"]},{"url":"https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48","name":"https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48","tags":["x_refsource_MISC"]},{"url":"https://github.com/caddyserver/caddy/releases/tag/v2.11.1","name":"https://github.com/caddyserver/caddy/releases/tag/v2.11.1","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"HIGH","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","baseScore":8.8,"baseSeverity":"HIGH","vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:P","version":"4.0"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-755","lang":"en","description":"CWE-755: Improper Handling of Exceptional Conditions","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-02-24T16:08:20.569Z"},"source":{"advisory":"GHSA-hffm-g8v7-wrv7","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-02-26T20:55:27.670740Z","id":"CVE-2026-27586","options":[{"Exploitation":"poc"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-02-26T20:56:20.526Z"}}]}}}