{"cve":"CVE-2026-27586","nvd":{"published":"2026-02-24T17:29:03.793","modified":"2026-06-17T10:27:20.880","status":"Analyzed","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.","cvss_v4":{"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","score":8.8},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","score":9.1},"cwes":["CWE-755"],"references":["https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48","https://github.com/caddyserver/caddy/releases/tag/v2.11.1","https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7"],"products":["caddyserver:caddy"],"source":"nvd","synced_at":"2026-10-19T22:24:17.937441719+00:00"},"epss":{"cve":"CVE-2026-27586","score":0.00295,"percentile":0.22146,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-hffm-g8v7-wrv7","url":"https://osv.dev/vulnerability/GHSA-hffm-g8v7-wrv7","summary":"Caddy: mTLS client authentication silently fails open when CA certificate file is missing or malformed","modified":"2026-02-27T19:52:41Z","packages":[{"ecosystem":"Go","name":"github.com/caddyserver/caddy/v2","purl":"pkg:golang/github.com/caddyserver/caddy/v2","ranges":["<2.11.1"],"fixed":["2.11.1"]}]},{"id":"GO-2026-4539","url":"https://osv.dev/vulnerability/GO-2026-4539","summary":"Caddy mTLS authentication fails open in github.com/caddyserver/caddy/v2","modified":"2026-02-26T19:11:17.562639Z","packages":[{"ecosystem":"Go","name":"github.com/caddyserver/caddy/v2","purl":"pkg:golang/github.com/caddyserver/caddy/v2","ranges":["<2.11.1"],"fixed":["2.11.1"]}]}],"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."]}