CVE-2026-34479
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.
Does this matter?
Lower severity and a low EPSS score (0.53%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 4.0
- 6.9 MEDIUMCVSS: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
- EPSS
- 0.53% probability · 44th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-116
- Affected
- apache/log4j
- Source
- security@apache.org
References
- https://github.com/apache/logging-log4j2/pull/4078Exploit, Issue Tracking, Patch
- https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5onMailing List
- https://logging.apache.org/cyclonedx/vdr.xmlVendor Advisory
- https://logging.apache.org/log4j/2.x/migrate-from-log4j1.htmlMitigation
- https://logging.apache.org/security.html#CVE-2026-34479Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/04/10/8Mailing List
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.