Caddy HTTP Host Matcher Casesensitivity Bypass (2.11.1)
CVE-2026-27588 Published on February 24, 2026

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

Github Repository Vendor Advisory NVD

Vulnerability Analysis

CVE-2026-27588 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. An automatable proof of concept (POC) exploit exists. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
NONE

Weakness Type

Improper Handling of Case Sensitivity

The software does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.


Products Associated with CVE-2026-27588

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Caddy Server Caddy Web Server
 

Affected Versions

caddyserver caddy Version < 2.11.1 is affected by CVE-2026-27588

Exploit Probability

EPSS
0.37%
Percentile
29.64%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.