TI-2026-21974 Aliases CVE-2026-27586 GHSA-hffm-g8v7-wrv7

Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed

HIGH 77CWE-755Published 2026-02-24 · Updated 2026-02-26

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Attack requirements: None
Impact type: —
Confidentiality · integrity · availability: High · High · None
Fix status: Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00295 22nd percentileScored 2026-11-07

Public exploit Yes 2 exploit referencesTagged by NVD

Fix Fixed caddy (caddyserver): 2.11.1github.com/caddyserver/caddy/v2 (Go): 2.11.1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
caddyserver	caddy	before 2.11.1	2.11.1	Patch available	CNA
—	github.com/caddyserver/caddy/v2 (Go)	before 2.11.1	2.11.1	Patch available	GHSA-hffm-g8v7-wrv7

caddy Vendorcaddyserver Affected before 2.11.1 Fixed in 2.11.1 Patch available CNA
github.com/caddyserver/caddy/v2 (Go) Vendor— Affected before 2.11.1 Fixed in 2.11.1 Patch available GHSA-hffm-g8v7-wrv7

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:caddyserver:caddy::::::::	before 2.11.1	Vulnerable	caddyserver

cpe:2.3:a:caddyserver:caddy:*:*:*:*:*:*:*:* Versions before 2.11.1 Vulnerable ·caddyserver

Remediation

Fix · CNA caddy (caddyserver) Fixed in 2.11.1
Fix · GHSA-hffm-g8v7-wrv7 github.com/caddyserver/caddy/v2 (Go) Fixed in 2.11.1 Advisory →

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product

Red Hat

Timeline

2026-10-02 Threatist record created from CVE-2026-27586
2026-10-03 Alias added: GHSA-hffm-g8v7-wrv7

References

Exploit 2

Advisory 1

https://nvd.nist.gov/vuln/detail/CVE-2026-27586

Other 4

TI-2023-23979 The HTTP/2 protocol allows a denial of service (server resource consumption) because… KEVCVSS 3.1HIGH 7.5
TI-2026-21978 Improper input validation in caddyserver caddy CVSS 4.0HIGH 8.9
TI-2026-23680 Improper authentication in caddyserver caddy CVSS 3.1HIGH 8.8
TI-2026-21976 Caddy: MatchHost becomes case-sensitive for large host lists (>100), enabling host-based route/auth bypass CVSS 4.0HIGH 7.7
TI-2026-21975 Caddy: MatchPath %xx (escaped-path) branch skips case normalization, enabling path-based route/auth bypass CVSS 4.0HIGH 7.7
TI-2026-37952 Caddy: Windows `file_server` path authorization bypass via encoded backslash CVSS 3.1HIGH 7.5

See all 19 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences