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CVE-2026-34479

7.5 · HIGH

The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output.

Published Apr 10, 2026CWE-116EPSS 0.91%

Overview

CVE-2026-34479 is a high-severity vulnerability. It was published on April 10, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records.

Two groups of users are affected:

* Those using Log4j1XmlLayout directly in a Log4j Core 2 configuration file.

* Those using the Log4j 1 configuration compatibility layer with org.apache.log4j.xml.XMLLayout specified as the layout class.

Users are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue.

Note: The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the Log4j 1 to Log4j 2 migration guide https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html , and specifically the section on eliminating reliance on the br

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/apache/logging-log4j2/pull/4078Reflists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5onReflogging.apache.org/cyclonedx/vdr.xmlReflogging.apache.org/log4j/2.x/migrate-from-log4j1.htmlReflogging.apache.org/security.html#CVE-2026-34479Refwww.openwall.com/lists/oss-security/2026/04/10/8

How CyberStrike helps

Frequently asked questions

What is CVE-2026-34479?

CVE-2026-34479 is a high-severity vulnerability. It was published on April 10, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-34479?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-34479?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-34479?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-34479 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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