CVE-2026-27586

HIGH EPSS 18.3%
Published Feb 24, 20264mo ago · Modified Feb 25, 20264mo ago
8.8 CVSS 4.0
High
Find Similar
Published Feb 24, 2026 4mo ago
Last Modified Feb 25, 2026 4mo ago

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 Details

Base Score
8.8
Exploitability
—
Impact
—
Vector string
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope X

Threat Intelligence

EPSS Exploit Probability
18.3% percentile
Exploit & Patch Status
Public Exploit Known
No Patch Available

Weaknesses 1

CWE-755

Affected Products 1

VendorProductVersionRange
caddyservercaddy* <2.11.1

References 3

  • gist.github.com https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48
    Exploit
  • github.com https://github.com/caddyserver/caddy/releases/tag/v2.11.1
    Release Notes
  • github.com https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7
    ExploitVendor Advisory

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.