capnproto Capn Proto up to 1.3.x HTTP Request Length request smuggling

Summaryinfo

A vulnerability, which was classified as problematic, was found in capnproto Capn Proto up to 1.3.x. This issue affects some unknown processing of the component HTTP Request Handler. The manipulation of the argument Length results in request smuggling. This vulnerability is reported as CVE-2026-32239. The attack can be launched remotely. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in capnproto Capn Proto up to 1.3.x. It has been classified as problematic. Affected is some unknown functionality of the component HTTP Request Handler. The manipulation of the argument Length with an unknown input leads to a request smuggling vulnerability. CWE is classifying the issue as 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. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

Cap'n Proto is a data interchange format and capability-based RPC system. Prior to 1.4.0, a negative Content-Length value was converted to unsigned, treating it as an impossibly large length instead. In theory, this bug could enable HTTP request/response smuggling. This vulnerability is fixed in 1.4.0.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-32239 since 03/11/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 302168 (Linux Distros Unpatched Vulnerability : CVE-2026-32239), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 1.4.0 eliminates this vulnerability. Applying the patch 2744b3c012b4aa3c31cefb61ec656829fa5c0e36 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at CNNVD (CNNVD-202603-2474) and Tenable (302168). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• capnproto

Name

• Capn Proto

Version

• 1.0
• 1.1
• 1.2
• 1.3

License

• open-source

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Once again VulDB remains the best source for vulnerability data.

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