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High severity7.5NVD Advisory· Published Apr 10, 2026· Updated May 6, 2026

CVE-2026-34479

CVE-2026-34479

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 bridge.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
org.apache.logging.log4j:log4j-1.2-apiMaven
>= 2.7, < 2.25.42.25.4
org.apache.logging.log4j:log4j-1.2-apiMaven
>= 3.0.0-beta1, <= 3.0.0-beta2—

Affected products

104

Patches

Vulnerability mechanics

References

8

News mentions

0

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