KAZUHO Starlet up to 0.31 on Perl Reverse Proxy Content-Length request smuggling

Summaryinfo

A vulnerability marked as critical has been reported in KAZUHO Starlet up to 0.31 on Perl. This impacts an unknown function of the component Reverse Proxy Handler. The manipulation of the argument Content-Length leads to request smuggling. This vulnerability is referenced as CVE-2026-40561. Remote exploitation of the attack is possible. No exploit is available. To fix this issue, it is recommended to deploy a patch.

Detailsinfo

A vulnerability, which was classified as critical, has been found in KAZUHO Starlet up to 0.31 on Perl. This issue affects an unknown code of the component Reverse Proxy Handler. The manipulation of the argument Content-Length with an unknown input leads to a request smuggling vulnerability. Using CWE to declare the problem leads to CWE-444. The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

The weakness was published by CPANSec. It is possible to read the advisory at datatracker.ietf.org. The identification of this vulnerability is CVE-2026-40561 since 04/14/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 311809 (Linux Distros Unpatched Vulnerability : CVE-2026-40561), which helps to determine the existence of the flaw in a target environment.

Applying the patch a7d5dfd1862aafa43e5eaca0fdb6acf4cc15b2d0 is able to eliminate this problem. The bugfix is ready for download at github.com.

The vulnerability is also documented in the databases at Tenable (311809) and EUVD (EUVD-2026-26806). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Vendor

• KAZUHO

Name

• Starlet

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8
• 0.9
• 0.10
• 0.11
• 0.12
• 0.13
• 0.14
• 0.15
• 0.16
• 0.17
• 0.18
• 0.19
• 0.20
• 0.21
• 0.22
• 0.23
• 0.24
• 0.25
• 0.26
• 0.27
• 0.28
• 0.29
• 0.30
• 0.31

License

• open-source

Website

• Product: https://github.com/kazuho/Starlet/

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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