CVE-2026-40561

Name: CVE-2026-40561
Creator: NVD / NIST
Published: 2026-05-03T01:15:58.39+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 0.38%

Last modified Jun 17, 2026

CVE-2026-40561 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. 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.. EPSS estimates a 0.38% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

0.38%

29.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-444

Affected Software

Vendor	Product	Versions
Kazuho	Starlet	<= 0.31

References

https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3Third Party Advisory
https://github.com/kazuho/Starlet/commit/a7d5dfd1862aafa43e5eaca0fdb6acf4cc15b2d0.patchPatch
https://metacpan.org/release/KAZUHO/Starlet-0.32/changes
http://www.openwall.com/lists/oss-security/2026/05/03/1Mailing List, Third Party Advisory

Timeline

Published: May 3, 2026
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2026-40561?

How severe is CVE-2026-40561?

CVE-2026-40561 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.38% probability of exploitation in the next 30 days.

How do I fix CVE-2026-40561?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-40561?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST