Caddy mTLS Auth Silent Fail Before v2.11.1
CVE-2026-27586 Published on February 24, 2026
Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
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.
Weakness Type
Improper Handling of Exceptional Conditions
The software does not handle or incorrectly handles an exceptional condition.
Products Associated with CVE-2026-27586
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Affected Versions
caddyserver caddy Version < 2.11.1 is affected by CVE-2026-27586Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.