CVE-2026-27590
CRITICAL9.8EPSS 0.24%Unicode case-folding causes incorrect split_path index in github.com/caddyserver/caddy/v2
Description
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.
Affected packages (3)
- Debian/caddyfrom 0
- Go/github.com/caddyserver/caddy/v2from 0, < 2.11.1
- Go/github.com/caddyserver/caddy/v2from 0, < 2.11.1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P |
| osv | CVSS 3.1 | CRITICAL9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
References (7)
- ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-27590
- ADVISORYhttps://security-tracker.debian.org/tracker/CVE-2026-27590
- PATCHhttps://github.com/caddyserver/caddy
- WEBhttps://github.com/caddyserver/caddy/releases/tag/v2.11.1
- WEBhttps://github.com/caddyserver/caddy/security/advisories/GHSA-5r3v-vc8m-m96g
- WEBhttps://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38
- WEBhttps://pkg.go.dev/vuln/GO-2026-4536