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.
How to fix
- apache log4j2.25.4 or later
- org.apache.logging.log4j:log4j-core2.25.4 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| apache log4j | 2.7 ≤ v < 2.25.4, 3.0.0 | 2.25.4 |
| org.apache.logging.log4j:log4j-coreMaven | 2.7 ≤ v < 2.25.4, 3.0.0-beta1 ≤ v ≤ 3.0.0-beta2 | 2.25.4 |
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