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[USN-8650-1] Cap'n Proto vulnerabilities

Posted on 19 August 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8650-1
August 19, 2026

capnproto vulnerabilities
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 26.04 LTS
- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS

Summary:

Several security issues were fixed in Cap'n Proto.

Software Description:
- 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)

Update instructions:

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

Ubuntu 26.04 LTS
libcapnp-1.1.0 1.1.0-2.1ubuntu0.1~esm1
Available with Ubuntu Pro
libcapnp-dev 1.1.0-2.1ubuntu0.1~esm1
Available with Ubuntu Pro

Ubuntu 24.04 LTS
libcapnp-1.0.1 1.0.1-4ubuntu0.1~esm1
Available with Ubuntu Pro
libcapnp-dev 1.0.1-4ubuntu0.1~esm1
Available with Ubuntu Pro

Ubuntu 22.04 LTS
libcapnp-0.8.0 0.8.0-2ubuntu2+esm1
Available with Ubuntu Pro
libcapnp-dev 0.8.0-2ubuntu2+esm1
Available with Ubuntu Pro

Ubuntu 20.04 LTS
libcapnp-0.7.0 0.7.0-6ubuntu0.1~esm1
Available with Ubuntu Pro
libcapnp-dev 0.7.0-6ubuntu0.1~esm1
Available with Ubuntu Pro

Ubuntu 18.04 LTS
libcapnp-0.6.1 0.6.1-1ubuntu1+esm1
Available with Ubuntu Pro
libcapnp-dev 0.6.1-1ubuntu1+esm1
Available with Ubuntu Pro

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

References:
https://ubuntu.com/security/notices/USN-8650-1
CVE-2026-32239, CVE-2026-32240

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