Vulnerability Details CVE-2026-27586
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.001
EPSS Ranking 17.8%
CVSS Severity
CVSS v3 Score 9.1
References
Products affected by CVE-2026-27586
-
cpe:2.3:a:caddyserver:caddy:0.10.0
-
cpe:2.3:a:caddyserver:caddy:0.10.1
-
cpe:2.3:a:caddyserver:caddy:0.10.10
-
cpe:2.3:a:caddyserver:caddy:0.10.11
-
cpe:2.3:a:caddyserver:caddy:0.10.12
-
cpe:2.3:a:caddyserver:caddy:0.10.13
-
cpe:2.3:a:caddyserver:caddy:0.10.14
-
cpe:2.3:a:caddyserver:caddy:0.10.2
-
cpe:2.3:a:caddyserver:caddy:0.10.3
-
cpe:2.3:a:caddyserver:caddy:0.10.4
-
cpe:2.3:a:caddyserver:caddy:0.10.5
-
cpe:2.3:a:caddyserver:caddy:0.10.6
-
cpe:2.3:a:caddyserver:caddy:0.10.7
-
cpe:2.3:a:caddyserver:caddy:0.10.8
-
cpe:2.3:a:caddyserver:caddy:0.10.9
-
cpe:2.3:a:caddyserver:caddy:0.11.0
-
cpe:2.3:a:caddyserver:caddy:0.11.1
-
cpe:2.3:a:caddyserver:caddy:0.5.0
-
cpe:2.3:a:caddyserver:caddy:0.5.1
-
cpe:2.3:a:caddyserver:caddy:0.6.0
-
cpe:2.3:a:caddyserver:caddy:0.7.0
-
cpe:2.3:a:caddyserver:caddy:0.7.1
-
cpe:2.3:a:caddyserver:caddy:0.7.2
-
cpe:2.3:a:caddyserver:caddy:0.7.3
-
cpe:2.3:a:caddyserver:caddy:0.7.4
-
cpe:2.3:a:caddyserver:caddy:0.7.5
-
cpe:2.3:a:caddyserver:caddy:0.7.6
-
cpe:2.3:a:caddyserver:caddy:0.8.0
-
cpe:2.3:a:caddyserver:caddy:0.8.1
-
cpe:2.3:a:caddyserver:caddy:0.8.2
-
cpe:2.3:a:caddyserver:caddy:0.8.3
-
cpe:2.3:a:caddyserver:caddy:0.9.0
-
cpe:2.3:a:caddyserver:caddy:0.9.1
-
cpe:2.3:a:caddyserver:caddy:0.9.2
-
cpe:2.3:a:caddyserver:caddy:0.9.3
-
cpe:2.3:a:caddyserver:caddy:0.9.4
-
cpe:2.3:a:caddyserver:caddy:0.9.5
-
cpe:2.3:a:caddyserver:caddy:1.0.0
-
cpe:2.3:a:caddyserver:caddy:1.0.1
-
cpe:2.3:a:caddyserver:caddy:1.0.2
-
cpe:2.3:a:caddyserver:caddy:1.0.3
-
cpe:2.3:a:caddyserver:caddy:1.0.4
-
cpe:2.3:a:caddyserver:caddy:1.0.5
-
cpe:2.3:a:caddyserver:caddy:2.0.0
-
cpe:2.3:a:caddyserver:caddy:2.1.0
-
cpe:2.3:a:caddyserver:caddy:2.1.1
-
cpe:2.3:a:caddyserver:caddy:2.10.0
-
cpe:2.3:a:caddyserver:caddy:2.10.1
-
cpe:2.3:a:caddyserver:caddy:2.10.2
-
cpe:2.3:a:caddyserver:caddy:2.11.0
-
cpe:2.3:a:caddyserver:caddy:2.2.0
-
cpe:2.3:a:caddyserver:caddy:2.2.1
-
cpe:2.3:a:caddyserver:caddy:2.2.3
-
cpe:2.3:a:caddyserver:caddy:2.3.0
-
cpe:2.3:a:caddyserver:caddy:2.4.0
-
cpe:2.3:a:caddyserver:caddy:2.4.1
-
cpe:2.3:a:caddyserver:caddy:2.4.2
-
cpe:2.3:a:caddyserver:caddy:2.4.3
-
cpe:2.3:a:caddyserver:caddy:2.4.4
-
cpe:2.3:a:caddyserver:caddy:2.4.5
-
cpe:2.3:a:caddyserver:caddy:2.4.6
-
cpe:2.3:a:caddyserver:caddy:2.5.0
-
cpe:2.3:a:caddyserver:caddy:2.5.1
-
cpe:2.3:a:caddyserver:caddy:2.5.2
-
cpe:2.3:a:caddyserver:caddy:2.6.0
-
cpe:2.3:a:caddyserver:caddy:2.6.1
-
cpe:2.3:a:caddyserver:caddy:2.6.2
-
cpe:2.3:a:caddyserver:caddy:2.6.3
-
cpe:2.3:a:caddyserver:caddy:2.6.4
-
cpe:2.3:a:caddyserver:caddy:2.7.0
-
cpe:2.3:a:caddyserver:caddy:2.7.1
-
cpe:2.3:a:caddyserver:caddy:2.7.2
-
cpe:2.3:a:caddyserver:caddy:2.7.3
-
cpe:2.3:a:caddyserver:caddy:2.7.4
-
cpe:2.3:a:caddyserver:caddy:2.7.5
-
cpe:2.3:a:caddyserver:caddy:2.7.6
-
cpe:2.3:a:caddyserver:caddy:2.8.0
-
cpe:2.3:a:caddyserver:caddy:2.8.1
-
cpe:2.3:a:caddyserver:caddy:2.8.2
-
cpe:2.3:a:caddyserver:caddy:2.8.3
-
cpe:2.3:a:caddyserver:caddy:2.8.4
-
cpe:2.3:a:caddyserver:caddy:2.9.0
-
cpe:2.3:a:caddyserver:caddy:2.9.1