Caddy: Unicode case-folding length expansion causes incorrect split_path index (SCRIPT_NAME/PATH_INFO confusion) in FastCGI transport
Summary
Caddy: Unicode case-folding length expansion causes incorrect split_path index (SCRIPT_NAME/PATH_INFO confusion) in FastCGI transport
Original description
The description as published by the source.
Caddy 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 index on a lowercased copy of the request path and then uses that byte index to slice the original path. This is unsafe for Unicode because strings.ToLower() can change UTF-8 byte length for some characters. As a result, Caddy can derive an incorrect SCRIPT_NAME/SCRIPT_FILENAME and PATH_INFO, potentially causing a request that contains .php to execute a different on-disk file than intended (path confusion). In setups where an attacker can control file contents (e.g., upload features), this can lead to unintended PHP execution of non-.php files (potential RCE depending on deployment). Version 2.11.1 fixes the issue.
Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-27590 caddy
- Ubuntu UBUNTU-CVE-2026-27590 caddy
References
- advisory github.com
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov
- web github.com