Severity: moderate Affected versions:
- Apache Log4j 1 to Log4j 2 bridge (org.apache.logging.log4j:log4j-1.2-api) 2.7 before 2.25.4 - Apache Log4j 1 to Log4j 2 bridge (org.apache.logging.log4j:log4j-1.2-api) 3.0.0-alpha1 through 3.0.0-beta2 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. 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. Credit: Ap4sh (Samy Medjahed) and Ethicxz (Eliott Laurie) (original reporters) (finder) jabaltarik1 (independently) (finder) References: https://github.com/apache/logging-log4j2/pull/4078 https://logging.apache.org/security.html#CVE-2026-34479 https://logging.apache.org/cyclonedx/vdr.xml https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html https://logging.apache.org/ https://www.cve.org/CVERecord?id=CVE-2026-34479 Timeline: 2026-02-16: Vulnerability reported by Ap4sh and ethicxz 2026-03-15: Independent report received from jabaltarik1 2026-03-24: Fix shared publicly by Piotr P. Karwasz as pull request #4078 2026-03-25: Fix verified by reporter 2026-03-28: Log4j 2.25.4 released
