9.1

CVE-2026-27588: caddyserver caddy Improper Handling of Case Sensitivity

CVSS: 9.1v3.1CriticalAnalyzed
AliasesUBUNTU-CVE-2026-27588DEBIAN-CVE-2026-27588GHSA-x76f-jf84-rqj8
Published 24-02-2026Last modified 27-02-2026
Open JSON

Vulnerability summary

CVE-2026-27588 is a critical (CVSS 9.1) Improper Handling of Case Sensitivity vulnerability in caddyserver caddy. EPSS estimates a 0.55% chance of exploitation in the next 30 days, higher than 45.1% of scored vulnerabilities. 1 public exploit is recorded.

Overall risk
70/100
0100
High · default modelHow is this calculated?
CVSS score
9.1/10
010
Critical · v3.1 (NVD)
EPSS score
0.55%
0%100%
Low · +0.18 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits1github

Advisory lineage

Upstream 0 · Downstream 2 · Related 2
OPENSUSE-SU-2026:21483-1SUSE-SU-2026:0757-1

Timeline

  1. 24-02-2026
    PublishedVulnerability first disclosed.
  2. 27-02-2026
    Last modifiedVulnerability information updated.

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 metrics

7 scores · 5 sources · 2 versions

EPSS trend

Probability

0.55%

Chance of exploitation in the next 30 days

Percentile

45%

Versus all other CVEs

30-day change

+0.18 pp

From 0.37% on 20-09-2026

20-09-202620-10-2026
EPSS score
0.55%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

1 found
  • githubUnverified

    Caddy

    Maturity: poc

Weaknesses

CWE · root cause

Affected systems

Caddyserver1 product
  • caddy< 2.11.1 | ≥ 2.10.2, < 2.11.1
Debian1 product
  • caddyAll versions (No fix recorded) | < 2.6.2-12+deb13u1 | < 2.11.2-1
Github.com/caddyserver/caddy1 product
  • v2< 2.11.1
Ubuntu1 product
  • caddyAll versions (No fix recorded)

4 vendors · 4 products

References

9 links