Vulnerability 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 Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Apache | Log4J | >= 2.7, < 2.25.4 |
Related Weaknesses (CWE)
References
- https://github.com/apache/logging-log4j2/pull/4078ExploitIssue TrackingPatch
- 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
FAQ
What is CVE-2026-34479?
CVE-2026-34479 is a vulnerability with a CVSS score of 7.5 (HIGH). 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 rejec...
How severe is CVE-2026-34479?
CVE-2026-34479 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-34479?
Check the references section above for vendor advisories and patch information. Affected products include: Apache Log4J.