{"id":"CVE-2026-34479","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-34479","generatedAt":"2026-10-28T05:02:33.879Z","title":"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.","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.","published":"2026-04-10T16:16:31.000Z","lastModified":"2026-10-26T21:10:00.000Z","status":"Analyzed","sourceIdentifier":"security@apache.org","cvss":{"version":"4.0","score":6.9,"severity":"MEDIUM","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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M"},"cwe":["CWE-116"],"affected":["apache/log4j"],"epss":{"score":0.00535,"percentile":0.44924,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (0.53%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://github.com/apache/logging-log4j2/pull/4078","tags":["Exploit","Issue Tracking","Patch"],"source":"security@apache.org"},{"url":"https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on","tags":["Mailing List"],"source":"security@apache.org"},{"url":"https://logging.apache.org/cyclonedx/vdr.xml","tags":["Vendor Advisory"],"source":"security@apache.org"},{"url":"https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html","tags":["Mitigation"],"source":"security@apache.org"},{"url":"https://logging.apache.org/security.html#CVE-2026-34479","tags":["Vendor Advisory"],"source":"security@apache.org"},{"url":"http://www.openwall.com/lists/oss-security/2026/04/10/8","tags":["Mailing List"],"source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-34479","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}