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.
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| maven | org.apache.logging.log4j:log4j-core | >= 2.7, < 2.25.4 | 2.25.4 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Apache | Log4j | from 2.7 before 2.25.4 Version 3.0.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-h383-gmxw-35v2
- https://nvd.nist.gov/vuln/detail/CVE-2026-34479
- 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
- http://www.openwall.com/lists/oss-security/2026/04/10/8