CVE-2026-34479
HighSummary
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. This may cause conforming XML parsers to reject documents, impacting log processing systems.
Risk Assessment
Organizations may encounter issues with log processing, potentially leading to data loss or errors in indexing records. Users utilizing Log4j1XmlLayout may be particularly vulnerable to these issues.
Recommendation
It is recommended to upgrade to version 2.25.4 of the Apache Log4j 1-to-Log4j 2 bridge, which addresses this issue. Users should also consider migrating to Log4j 2, as the bridge is deprecated.
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Original NVD description (English source)
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

