# CVE-2026-40561: starlet: Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence

CVE-2026-40561 is fixed in starlet on 1 platform, first by DEBIAN-CVE-2026-40561, released May 15, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-40561
- Priority: Routine
- CVSS: 5.3 (medium)
- EPSS: 0.0036
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 3, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | starlet Debian 13.5 (trixie) | 0.31-2+deb13u1 | [DEBIAN-CVE-2026-40561](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40561.md) | May 15, 2026 |
| Linux | starlet Debian 14 | 0.31-3 | [DEBIAN-CVE-2026-40561](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40561.md) | May 15, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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