High 8.9Published Feb 24, 2026

CVE-2026-27590Caddy: Unicode case-folding length expansion causes incorrect split_path index (SCRIPT_NAME/PATH_INFO confusion) in FastCGI transport

Updated under an hour ago (Oct 28, 2026, 6:50 AM ET)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 8.9 HIGH (v4.0, CNA)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
Weakness (CWE): CWE-20, CWE-180
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Feb 27, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

caddyserver caddy caddyserver:caddy (from the name)	before 2.11.1	CNA record
caddyserver caddy caddyserver:caddy	before 2.11.1	NVD

References

References

https://github.com/caddyserver/caddy/security/advisories/GHSA-5r3v-vc8m-m96g	x-refsource-confirm, exploit, vendor-advisory
https://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38	x-refsource-misc, third-party-advisory
https://github.com/caddyserver/caddy/releases/tag/v2.11.1	x-refsource-misc, release-notes

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.