{"cve":"CVE-2026-34479","nvd":{"published":"2026-04-10T16:16:31.270","modified":"2026-10-26T21:10:00.170","status":"Analyzed","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\n\nUsers are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue.\n\nNote: 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.","cvss_v4":{"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},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","score":7.5},"cwes":["CWE-116"],"references":["https://github.com/apache/logging-log4j2/pull/4078","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"],"products":["apache:log4j"],"source":"nvd","synced_at":"2026-10-26T21:38:48.864438205+00:00"},"epss":{"cve":"CVE-2026-34479","score":0.00535,"percentile":0.44858,"date":"2026-10-26"},"kev":null,"osv":[{"id":"GHSA-h383-gmxw-35v2","url":"https://osv.dev/vulnerability/GHSA-h383-gmxw-35v2","summary":"Apache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters","modified":"2026-10-26T15:30:05.719203570Z","packages":[{"ecosystem":"Maven","name":"org.apache.logging.log4j:log4j-core","purl":"pkg:maven/org.apache.logging.log4j/log4j-core","ranges":[">=2.7 <2.25.4"],"fixed":["2.25.4"]},{"ecosystem":"Maven","name":"org.apache.logging.log4j:log4j-core","purl":"pkg:maven/org.apache.logging.log4j/log4j-core","ranges":[">=3.0.0-beta1 <=3.0.0-beta2"],"fixed":[]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}