Critical severity · published Feb 24, 2026
CVE-2026-27586
Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
9.1
CVSS
0.3%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 22% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CA
caddy · caddyserver
< 2.11.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27586
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-27586
Exploit
https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48
Release Notes
https://github.com/caddyserver/caddy/releases/tag/v2.11.1
Exploit
https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7
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