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Vulnerability record · CVE-2026-27588 · published 24 February 2026

CVE-2026-27588: Caddyserver caddy vulnerability

Caddyserver · Caddy

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.

7.7 CVSS 4.0 High EPSS 0.54% · top 56.8% CWE-178 · CWE-178
7.7CVSS 4.0 base score
0.54%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References, 1 tagged exploit
17 Jun 2026Last modified by NVD

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: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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/caddyserver/caddy/releases/tag/v2.11.1 Release Notes
https://github.com/caddyserver/caddy/security/advisories/GHSA-x76f-jf84-rqj8 ExploitVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

7.5CVE-2023-44487HTTP/2 Rapid Reset stream cancellation denial of serviceThe HTTP/2 protocol permits a client to cancel many streams quickly, and the server's handling of those resets consumes disproportionate resources. T…KEVEPSS 100%analysed9.8CVE-2018-21246Caddyserver caddy improper authentication vulnerabilityCaddy before 0.10.13 mishandles TLS client authentication, as demonstrated by an authentication bypass caused by the lack of the StrictHostMatching m…EPSS 2.7%8.9CVE-2026-27590Caddyserver caddy improper input validation vulnerabilityCaddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's FastCGI path splitting logic computes the split ind…EPSS 0.86%8.8CVE-2026-30851Caddyserver caddy improper authentication vulnerabilityCaddy is an extensible server platform that uses TLS by default. From version 2.10.0 to before version 2.11.2, forward_auth copy_headers does not str…EPSS 0.35%8.8CVE-2026-27586Caddyserver caddy vulnerabilityCaddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, two swallowed errors in `ClientAuthentication.provision()` …EPSS 0.40%8.1CVE-2026-52845Caddyserver caddy improper authentication vulnerabilityCaddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the exact client-supplied identit…EPSS 0.45%8.1CVE-2026-45135Caddyserver caddy improper input validation vulnerabilityCaddy is an extensible server platform that uses TLS by default. From 2.7.0 until 2.11.3, the FastCGI transport's splitPos() in modules/caddyhttp/rev…EPSS 0.68%7.7CVE-2026-27587Caddyserver caddy vulnerabilityCaddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's HTTP `path` request matcher is intended to be case-…EPSS 0.54%

Source: NIST National Vulnerability Database (record CVE-2026-27588), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.