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[USN-8954-1] zlib vulnerability

Posted on 22 October 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8954-1
October 22, 2026

zlib vulnerability
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 26.10
- Ubuntu 26.04 LTS
- Ubuntu 24.04 LTS

Summary:

zlib could be made to crash or run programs if it received specially
crafted input.

Software Description:
- zlib: Lossless data-compression library

Details:

Ali Firas discovered that zlib incorrectly handled certain non-blocking
write operations. An attacker could possibly use this issue to trigger a
heap buffer overflow, resulting in a denial of service or arbitrary code
execution.

Update instructions:

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

Ubuntu 26.10
lib32z1 1:1.3.dfsg+really1.3.2-3ubuntu1.1
lib32z1-dev 1:1.3.dfsg+really1.3.2-3ubuntu1.1
lib64z1 1:1.3.dfsg+really1.3.2-3ubuntu1.1
lib64z1-dev 1:1.3.dfsg+really1.3.2-3ubuntu1.1
libx32z1 1:1.3.dfsg+really1.3.2-3ubuntu1.1
libx32z1-dev 1:1.3.dfsg+really1.3.2-3ubuntu1.1
zlib1g 1:1.3.dfsg+really1.3.2-3ubuntu1.1
zlib1g-dev 1:1.3.dfsg+really1.3.2-3ubuntu1.1

Ubuntu 26.04 LTS
lib32z1 1:1.3.dfsg+really1.3.1-1ubuntu3.2
lib32z1-dev 1:1.3.dfsg+really1.3.1-1ubuntu3.2
lib64z1 1:1.3.dfsg+really1.3.1-1ubuntu3.2
lib64z1-dev 1:1.3.dfsg+really1.3.1-1ubuntu3.2
libx32z1 1:1.3.dfsg+really1.3.1-1ubuntu3.2
libx32z1-dev 1:1.3.dfsg+really1.3.1-1ubuntu3.2
zlib1g 1:1.3.dfsg+really1.3.1-1ubuntu3.2
zlib1g-dev 1:1.3.dfsg+really1.3.1-1ubuntu3.2

Ubuntu 24.04 LTS
lib32z1 1:1.3.dfsg-3.1ubuntu2.3
lib32z1-dev 1:1.3.dfsg-3.1ubuntu2.3
lib64z1 1:1.3.dfsg-3.1ubuntu2.3
lib64z1-dev 1:1.3.dfsg-3.1ubuntu2.3
libx32z1 1:1.3.dfsg-3.1ubuntu2.3
libx32z1-dev 1:1.3.dfsg-3.1ubuntu2.3
zlib1g 1:1.3.dfsg-3.1ubuntu2.3
zlib1g-dev 1:1.3.dfsg-3.1ubuntu2.3

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

References:
https://ubuntu.com/security/notices/USN-8954-1
CVE-2026-85091

Package Information:
https://launchpad.net/ubuntu/+source/zlib/1:1.3.dfsg+really1.3.2-3ubuntu1.1
https://launchpad.net/ubuntu/+source/zlib/1:1.3.dfsg+really1.3.1-1ubuntu3.2
https://launchpad.net/ubuntu/+source/zlib/1:1.3.dfsg-3.1ubuntu2.3

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