USN-8650-1: Cap'n Proto vulnerabilities

Publication date

19 August 2026

Overview

Several security issues were fixed in Cap'n Proto.


Packages

  • capnproto - Fast data interchange format and capability-based RPC system

Details

Chanho Kim and Jihyeok Han discovered that Cap'n Proto incorrectly
handled negative Content-Length values or excessively large chunk sizes
when processing HTTP messages. An attacker could possibly use these
issues to cause HTTP messages to be interpreted inconsistently,
resulting in HTTP request or response smuggling. (CVE-2026-32239,
CVE-2026-32240)

Chanho Kim and Jihyeok Han discovered that Cap'n Proto incorrectly
handled negative Content-Length values or excessively large chunk sizes
when processing HTTP messages. An attacker could possibly use these
issues to cause HTTP messages to be interpreted inconsistently,
resulting in HTTP request or response smuggling. (CVE-2026-32239,
CVE-2026-32240)

Update instructions

In general, a standard system update will make all the necessary changes.

Learn more about how to get the fixes.

The problem can be corrected by updating your system to the following package versions:

Ubuntu Release Package Version
26.04 LTS resolute libcapnp-1.1.0 –  1.1.0-2.1ubuntu0.1~esm1  
libcapnp-dev –  1.1.0-2.1ubuntu0.1~esm1  
24.04 LTS noble libcapnp-1.0.1 –  1.0.1-4ubuntu0.1~esm1  
libcapnp-dev –  1.0.1-4ubuntu0.1~esm1  
22.04 LTS jammy libcapnp-0.8.0 –  0.8.0-2ubuntu2+esm1  
libcapnp-dev –  0.8.0-2ubuntu2+esm1  
20.04 LTS focal libcapnp-0.7.0 –  0.7.0-6ubuntu0.1~esm1  
libcapnp-dev –  0.7.0-6ubuntu0.1~esm1  
18.04 LTS bionic libcapnp-0.6.1 –  0.6.1-1ubuntu1+esm1  
libcapnp-dev –  0.6.1-1ubuntu1+esm1  

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