CVE-2026-34479

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.

• CWE-116

• https://github.com/apache/logging-log4j2/pull/4078Exploit, Issue Tracking, Patch
• https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5onMailing List
• https://logging.apache.org/cyclonedx/vdr.xmlVendor Advisory
• https://logging.apache.org/log4j/2.x/migrate-from-log4j1.htmlMitigation
• https://logging.apache.org/security.html#CVE-2026-34479Vendor Advisory
• http://www.openwall.com/lists/oss-security/2026/04/10/8Mailing List

Published

Apr 10, 2026

Last Modified

Jun 17, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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