CVE-2026-34479
Apache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters
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
Log4j1XmlLayoutdirectly in a Log4j Core 2 configuration file. - Those using the Log4j 1 configuration compatibility layer with
org.apache.log4j.xml.XMLLayoutspecified 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, and specifically the section on eliminating reliance on the bridge.
Patch Available
Fix available through Seal Security. No upgrade required, protect your application instantly.
