What is the CVSS score of CVE-2026-27586?

CVE-2026-27586 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.1%.

Which versions of TLS are affected by CVE-2026-27586?

Caddy servers prior to version 2.11.1 fail silently when mutual TLS (mTLS) client certificate validation encounters errors, allowing unauthorized clients to bypass authentication entirely.. A patch is available.

Is there a public PoC exploit available for CVE-2026-27586?

Yes, a public proof-of-concept exploit is available for CVE-2026-27586. Prioritise patching immediately. EPSS: 0.1%.

How to fix or mitigate CVE-2026-27586?

Within 24 hours: Inventory all Caddy deployments and document versions; audit CA certificate files for missing or corrupted entries; enable detailed logging of authentication failures. Within 7 days: Test upgrade path to Caddy 2.11.1 or later in non-production environments; validate mTLS handshake logs to confirm authentication is enforced. Within 30 days: Deploy patched Caddy version across all production environments; conduct penetration testing to validate that certificate validation failures now reject rather than allow connections.

TLS CVE-2026-27586

CRITICAL

Improper Handling of Exceptional Conditions (CWE-755)

2026-02-24 security-advisories@github.com

GHSA-hffm-g8v7-wrv7

TLS Caddy Suse

9.1

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

9.1 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

SUSE

CRITICAL

qualitative

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

Analysis Generated

Mar 12, 2026 - 21:55 vuln.today

PoC Detected

Feb 25, 2026 - 17:14 vuln.today

Public exploit code

CVE Published

Feb 24, 2026 - 17:29 nvd

CRITICAL 9.1

DescriptionGitHub Advisory

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.

AnalysisAI

TLS error swallowing in Caddy web server before 2.11.1 allows bypassing client certificate authentication. Errors in ClientCAs handling are silenced, potentially accepting invalid client certificates. PoC available.

Technical ContextAI

CWE-755 improper handling of exceptional conditions. Two error paths in ClientHelloInfo and ClientAuth handling are silently ignored, potentially accepting connections that should be rejected.

RemediationAI

Update to Caddy 2.11.1. Verify mTLS configurations are properly enforcing certificate validation.

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Same weakness CWE-755 – Improper Handling of Exceptional Conditions

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Vendor StatusVendor

SUSE

Severity: Critical

Product	Status
openSUSE Leap 15.6	Fixed
SUSE Linux Enterprise Module for Package Hub 15 SP5	Fixed
SUSE Linux Enterprise Module for Package Hub 15 SP6	Fixed
openSUSE Leap 15.5	Fixed

CVE-2026-27586 vulnerability details – vuln.today

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TLS CVE-2026-27586

Severity by source

CVSS VectorGitHub Advisory

Lifecycle Timeline

DescriptionGitHub Advisory

AnalysisAI

Technical ContextAI

RemediationAI

More in TLS

Same weakness CWE-755 – Improper Handling of Exceptional Conditions

Vendor StatusVendor

SUSE

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External POC / Exploit Code