CVE-2026-27586: Caddyserver Caddy

Critical severity, CVSS 9.1. EPSS: 0.4% chance of exploitation in the next 30 days.

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 products

• Caddyserver Caddy: before 2.11.1 (fixed in 2.11.1)

Published 2026-02-24. Last modified 2026-06-17.