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CVE-2026-27586

Caddyserver Caddy vulnerability

9.1 CRITICALPublic exploitEPSS 0.40%
  1. Published24 Feb 2026

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 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Caddyserver Caddy< 2.11.1

Remediation

Fixed in
Caddyserver Caddy≥ 2.11.1

References

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Frequently asked

Is CVE-2026-27586 being actively exploited?

CVE-2026-27586 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.40%.

How severe is CVE-2026-27586?

CVE-2026-27586 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.40% probability of exploitation.

Which products are affected by CVE-2026-27586?

Affected products include Caddyserver Caddy.

How do I fix CVE-2026-27586?

Upgrade affected software to a fixed version, for example Caddyserver Caddy 2.11.1 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-27586 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.