Paper/Archive/CVE-2026-27588

CVE-2026-27588

caddyserver caddy — Caddy: MatchHost becomes case-sensitive for large host lists (>100), enabling host-based route/auth bypass

EPSS 0.4%public exploit CVSS 9.1

critical.is priorityof 100

CVSS 9.1 (NVD)9.1 / 10 × 3027.3 Not in CISA KEV+300.0 EPSS percentile 36.8.368 × 207.4 Exploit: SSVC poc+1010.0 SSVC exploitation: poc+100.0

Description · from the CVE record

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.

Affected

ProductAffectedFixed inSource

caddy< 2.11.1–CNA

Scores by source

NVD9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

GitHub_M (CNA)7.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P

CISA ADPSSVCExploitation: poc · Automatable: yes · Technical impact: partial

References

refgithub.com/caddyserver/caddy/security/advisories/GHSA-x76f-jf84-rqj8 refgithub.com/caddyserver/caddy/releases/tag/v2.11.1