CVE-2026-27586

The record

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 packages

Related vulnerabilities

• GO-2026-4539 Caddy mTLS authentication fails open in github.com/caddyserver/caddy/v2 Same vulnerability
• GO-2026-4535 Improper sanitization of glob characters in github.com/caddyserver/caddy/v2 Also affects github.com/caddyserver/caddy/v2
• GO-2026-4536 Unicode case-folding causes incorrect split_path index in github.com/caddyserver/caddy/v2 Also affects github.com/caddyserver/caddy/v2
• GO-2026-4537 Caddy is vulnerable to cross-origin config application via local admin API /load in… Also affects github.com/caddyserver/caddy/v2
• GO-2026-4541 Caddy MatchHost becomes case-sensitive in github.com/caddyserver/caddy/v2 Also affects github.com/caddyserver/caddy/v2
• GO-2026-4538 Caddy MatchPath %xx branch skips case normalization in github.com/caddyserver/caddy/v2 Also affects github.com/caddyserver/caddy/v2
• CVE-2026-27589 Caddy is an extensible server platform that uses TLS by default. Also affects github.com/caddyserver/caddy/v2
• CVE-2026-27588 Caddy is an extensible server platform that uses TLS by default. Also affects github.com/caddyserver/caddy/v2