Improper input validation in Caddyserver Caddy
CVE-2026-27590
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.
Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.009 (58.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 58th percentile — 58.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.009 · change: +0.003
Affected products
- Caddyserver Caddy — versions < 2.11.1
Weakness classification (CWE)
References
- github.com/caddyserver/caddy/security/advisories/GHSA-5r3v-vc8m-m96g (Exploit, Vendor Advisory)
- github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38 (Third Party Advisory)
- github.com/caddyserver/caddy/releases/tag/v2.11.1 (Release Notes)
Frequently asked questions
- What is CVE-2026-27590?
- CVE-2026-27590 is a critical-severity vulnerability in Caddyserver Caddy, classified under Improper Input Validation. CVSS score: 9.8/10. Published 2026-02-24.
- How severe is CVE-2026-27590?
- Critical severity. CVSS v3 base score is 9.8 out of 10.