Cap'n Proto has an integer overflow in KJ-HTTP

[nixpkgs-security-tracker]

• CVE-2026-32239
• Nixpkgs security tracker issue
• affected package maintainers: cc @lf-, @9999years, @RaitoBezarius, @Qyriad, @alois31

Description

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.

Affected packages

• capnproto (1.2.0@nixos-25.11, 1.2.0@nixos-unstable)

Additional comment

Upstream advisory: https://github.com/capnproto/capnproto/security/advisories/GHSA-qjx3-pp3m-9jpm