CVE-2026-34479Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters

Descripción

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.

Datos: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Se publican tal como los indican las fuentes, en inglés.

Productos y versiones afectados

Referencias y parches

• https://github.com/apache/logging-log4j2/pull/4078 patchExploitIssue TrackingPatch
• https://logging.apache.org/security.html#CVE-2026-34479 vendor-advisoryVendor Advisory
• https://logging.apache.org/cyclonedx/vdr.xml vendor-advisoryVendor Advisory
• https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html relatedMitigation
• https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on vendor-advisoryMailing List
• http://www.openwall.com/lists/oss-security/2026/04/10/8 Mailing List