{"id":"GHSA-h383-gmxw-35v2","aliases":["CVE-2026-34479"],"title":"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.\n\nTwo groups of users are affected:\n\n* Those using `Log4j1XmlLayout` directly in a Log4j Core 2 configuration file.\n* Those using the Log4j 1 configuration compatibility layer with `org.apache.log4j.xml.XMLLayout` specified as the layout class.\n\nUsers are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version `2.25.4`, which corrects this issue.\n\n> [!NOTE]\n> The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the\n> [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bridge.","severity":"medium","score":6.9,"published":"2026-04-10T18:31:18.000Z","modified":"2026-10-26T15:30:05.719Z","withdrawn":false,"knownExploited":false,"affected":[{"ecosystem":"Maven","name":"org.apache.logging.log4j:log4j-core","ranges":[{"events":[{"introduced":"2.7"},{"fixed":"2.25.4"}],"type":"ECOSYSTEM"}],"versions":["2.10.0","2.11.0","2.11.1","2.11.2","2.12.0","2.12.1","2.12.2","2.12.3","2.12.4","2.13.0","2.13.1","2.13.2","2.13.3","2.14.0","2.14.1","2.15.0","2.16.0","2.17.0","2.17.1","2.17.2","2.18.0","2.19.0","2.20.0","2.21.0","2.21.1","2.22.0","2.22.1","2.23.0","2.23.1","2.24.0","2.24.1","2.24.2","2.24.3","2.25.0","2.25.1","2.25.2","2.25.3","2.7","2.8","2.8.1","2.8.2","2.9.0","2.9.1"],"fixed":["2.25.4"]},{"ecosystem":"Maven","name":"org.apache.logging.log4j:log4j-core","ranges":[{"events":[{"introduced":"3.0.0-beta1"},{"last_affected":"3.0.0-beta2"}],"type":"ECOSYSTEM"}],"versions":["3.0.0-beta1","3.0.0-beta2"],"fixed":[]}],"references":["https://nvd.nist.gov/vuln/detail/CVE-2026-34479","https://github.com/apache/logging-log4j2/pull/4078","https://github.com/apache/logging-log4j2","https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on","https://logging.apache.org/cyclonedx/vdr.xml","https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html","https://logging.apache.org/security.html#CVE-2026-34479","http://www.openwall.com/lists/oss-security/2026/04/10/8"],"sources":[{"name":"OSV","id":"GHSA-h383-gmxw-35v2","modified":"2026-10-26T15:30:05.719203570Z","url":"https://osv.dev/vulnerability/GHSA-h383-gmxw-35v2"}],"assessments":[{"source":"OSV","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N","score":6.9}]}