Vulnerability · Published May 3, 2026 · Assigned by CPANSec
CVE-2026-40561Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence
Medium 5.3
In plain English
A medium-severity security flaw in Starlet from KAZUHO. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 30% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Starlet incorrectly prioritizes "Content-Length" over "Transfer-Encoding: chunked" when both headers are present in an HTTP request. Per RFC 7230 3.3.3, Transfer-Encoding must take precedence. An attacker could exploit this to smuggle malicious HTTP requests via a front-end reverse proxy.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | perl-starlet | 0.32-r0 | ALPINE-CVE-2026-40561 |
| Alpine:v3.24 | perl-starlet | 0.32-r0 | ALPINE-CVE-2026-40561 |
| Debian:12 | starlet | no fix listed | DEBIAN-CVE-2026-40561 |
| Debian:13 | starlet | 0.31-2+deb13u1 | DEBIAN-CVE-2026-40561 |
| Debian:14 | starlet | 0.31-3 | DEBIAN-CVE-2026-40561 |
| Ubuntu:22.04:LTS | starlet | no fix listed | UBUNTU-CVE-2026-40561 |
| Ubuntu:24.04:LTS | starlet | no fix listed | UBUNTU-CVE-2026-40561 |
| Ubuntu:25.10 | starlet | no fix listed | UBUNTU-CVE-2026-40561 |
| Ubuntu:26.04:LTS | starlet | no fix listed | UBUNTU-CVE-2026-40561 |
| Ubuntu:26.10 | starlet | no fix listed | UBUNTU-CVE-2026-40561 |
Affected products (as reported)
Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N