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Critical severity · published Feb 24, 2026
CVE-2026-27588
Caddy: MatchHost becomes case-sensitive for large host lists (>100), enabling host-based route/auth bypass
9.1
CVSS
0.4%
EPSS
No
On KEV
Description
Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's HTTP `host` request matcher is documented as case-insensitive, but when configured with a large host list (>100 entries) it becomes case-sensitive due to an optimized matching path. An attacker can bypass host-based routing and any access controls attached to that route by changing the casing of the `Host` header. Version 2.11.1 contains a fix for the issue.
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)0.4% · higher than 37% 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
Affected product
CA
caddy
caddyserver
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27588
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-27588
Release Notes
https://github.com/caddyserver/caddy/releases/tag/v2.11.1
Exploit
https://github.com/caddyserver/caddy/security/advisories/GHSA-x76f-jf84-rqj8
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