What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-03 · updated 2026-10-26
• Weakness: CWE-444

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 products

• KAZUHO Starlet: through 0.31

References

• https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3
• https://github.com/kazuho/Starlet/commit/a7d5dfd1862aafa43e5eaca0fdb6acf4cc15b2d0.patch
• https://metacpan.org/release/KAZUHO/Starlet-0.32/changes
• http://www.openwall.com/lists/oss-security/2026/05/03/1

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