CVE-2026-27587 Caddy: MatchPath %xx (escaped-path) branch skips case normalization, enabling path-based route/auth bypass
Attackers can bypass path-based routing and access controls in Caddy by manipulating case in percent-encoded paths.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27587?
CVE-2026-27587 is a high-severity vulnerability in caddyserver caddy, published on 24 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Caddy 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-insensitive, but when the match pattern contains percent-escape sequences (`%xx`) it compares against the request's escaped path without lowercasing. An attacker can bypass path-based routing and any access controls attached to that route by changing the casing of the request path. Version 2.11.1 contains a fix for the issue.
Weakness: CWE-178
Which versions are affected by CVE-2026-27587?
3 open source packages ship an affected version, including github.com/caddyserver/caddy/v2. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/caddyserver/caddy/v2 Go | All versions | 2.11.1 |
github.com/caddyserver/caddy/v2 Go | All versions | 2.11.1 |
github.com/caddyserver/caddy/v2 Go | All versions | 2.11.1 |
Products include Caddyserver Caddy.
How do I fix CVE-2026-27587?
Upgrade github.com/caddyserver/caddy/v2 to 2.11.1 or later.
Is CVE-2026-27587 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27587 exists.
Other vulnerabilities in caddyserver caddy
- CVE-2018-21246 Caddy vulnerable to Authentication Bypass due to mishandling of TLS client authentication
- CVE-2026-27590 Caddy: Unicode case-folding length expansion causes incorrect split_path index in FastCGI transport
- CVE-2026-27586 Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
- CVE-2026-45135 Caddy: Unsafe Unicode Handling in FastCGI splitPos Allows Execution of Non-PHP Files
- CVE-2026-52845 Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
Sources
Also known as DEBIAN-CVE-2026-27587, GHSA-g7pc-pc7g-h8jh, GO-2026-4538, MINI-qpp3-fxrg-82v7, UBUNTU-CVE-2026-27587.