CVE-2026-40560: starman Request Smuggling — Fix

Description

Starman versions before 0.4018 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Starman 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.

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CVSS v3.1 Score

7.5

HIGH

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

EPSS — Exploit Prediction

0.0002

Probability of exploitation

0.03%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-444 CWE-444

Affected Products

Vendor	Product	Versions
miyagawa	starman	< 0.4018

References

Advisories & Patches

https://github.com/miyagawa/Starman/commit/ced205f0805027e9d9c0731f8c40b104220604ed.patch

Other References

https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3 https://metacpan.org/release/MIYAGAWA/Starman-0.4018/changes http://www.openwall.com/lists/oss-security/2026/04/29/1

Frequently Asked Questions

What is CVE-2026-40560? +

Starman versions before 0.4018 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Starman 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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-40560? +

CVE-2026-40560 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0002, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-40560? +

CVE-2026-40560 affects products from miyagawa, specifically: starman. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-40560? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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