1. Ubuntu Security Notices
  2. USN-8790-1

USN-8790-1: Expat vulnerabilities

Publication date

21 September 2026

Overview

Several security issues were fixed in Expat.

Releases

Packages

  • expat - XML parsing C library

Details

It was discovered that Expat could be made to allocate large amounts of
memory when parsing a small crafted document. An attacker could possibly
use this issue to cause Expat to consume resources, leading to a denial of
service. This issue was only addressed in Ubuntu 24.04 LTS.
(CVE-2025-59375)

It was discovered that Expat incorrectly handled empty external parameter
entity content. An attacker could possibly use this issue to cause Expat to
crash, resulting in a denial of service. (CVE-2026-32776)

It was discovered that Expat incorrectly handled certain DTD content. An
attacker could possibly use this issue to cause Expat to enter an infinite
loop, resulting in a denial of service. (CVE-2026-32777)

It was discovered that Expat incorrectly handled memory when retrying after
an earlier out-of-memory...

It was discovered that Expat could be made to allocate large amounts of
memory when parsing a small crafted document. An attacker could possibly
use this issue to cause Expat to consume resources, leading to a denial of
service. This issue was only addressed in Ubuntu 24.04 LTS.
(CVE-2025-59375)

It was discovered that Expat incorrectly handled empty external parameter
entity content. An attacker could possibly use this issue to cause Expat to
crash, resulting in a denial of service. (CVE-2026-32776)

It was discovered that Expat incorrectly handled certain DTD content. An
attacker could possibly use this issue to cause Expat to enter an infinite
loop, resulting in a denial of service. (CVE-2026-32777)

It was discovered that Expat incorrectly handled memory when retrying after
an earlier out-of-memory condition. An attacker could possibly use this
issue to cause Expat to crash, resulting in a denial of service.
(CVE-2026-32778)

It was discovered that Expat performed attribute name collision checks
inefficiently. An attacker could possibly use this issue to cause Expat to
consume resources when processing a moderately sized crafted XML document,
resulting in a denial of service. This issue was only addressed in Ubuntu
24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-45186)

It was discovered that Expat used insufficient entropy, allowing hash
flooding through a crafted XML document. An attacker could possibly use
this issue to cause Expat to consume resources, leading to a denial of
service. This issue was only addressed in Ubuntu 14.04 LTS, Ubuntu 24.04
LTS, and Ubuntu 26.04 LTS. (CVE-2026-41080)

It was discovered that Expat did not track handler call depth for certain
functions called from within handlers, leading to a use-after-free. An
attacker could possibly use this issue to cause Expat to crash, resulting
in a denial of service, or possibly execute arbitrary code.
(CVE-2026-50219, CVE-2026-56412)

It was discovered that Expat incorrectly handled certain values, leading to
integer overflows. An attacker could possibly use this issue to cause Expat
to crash, resulting in a denial of service. (CVE-2026-56403,
CVE-2026-56404, CVE-2026-56405)

It was discovered that Expat incorrectly handled certain values, leading to
an integer overflow. An attacker could possibly use this issue to cause
Expat to crash, resulting in a denial of service. This issue only affected
Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and
Ubuntu 26.04 LTS. (CVE-2026-56408)

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 expat –  2.7.4-1ubuntu0.1
libexpat1 –  2.7.4-1ubuntu0.1
libexpat1-dev –  2.7.4-1ubuntu0.1
24.04 LTS noble expat –  2.6.1-2ubuntu0.5
libexpat1 –  2.6.1-2ubuntu0.5
libexpat1-dev –  2.6.1-2ubuntu0.5
22.04 LTS jammy expat –  2.4.7-1ubuntu0.8
libexpat1 –  2.4.7-1ubuntu0.8
libexpat1-dev –  2.4.7-1ubuntu0.8
20.04 LTS focal expat –  2.2.9-1ubuntu0.8+esm2  
libexpat1 –  2.2.9-1ubuntu0.8+esm2  
libexpat1-dev –  2.2.9-1ubuntu0.8+esm2  
18.04 LTS bionic expat –  2.2.5-3ubuntu0.9+esm4  
libexpat1 –  2.2.5-3ubuntu0.9+esm4  
libexpat1-dev –  2.2.5-3ubuntu0.9+esm4  
16.04 LTS xenial expat –  2.1.0-7ubuntu0.16.04.5+esm13  
lib64expat1 –  2.1.0-7ubuntu0.16.04.5+esm13  
lib64expat1-dev –  2.1.0-7ubuntu0.16.04.5+esm13  
libexpat1 –  2.1.0-7ubuntu0.16.04.5+esm13  
libexpat1-dev –  2.1.0-7ubuntu0.16.04.5+esm13  
14.04 LTS trusty expat –  2.1.0-4ubuntu1.4+esm12  
lib64expat1 –  2.1.0-4ubuntu1.4+esm12  
lib64expat1-dev –  2.1.0-4ubuntu1.4+esm12  
libexpat1 –  2.1.0-4ubuntu1.4+esm12  
libexpat1-dev –  2.1.0-4ubuntu1.4+esm12  

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References

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