Apache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters
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
Log4j1XmlLayoutdirectly in a Log4j Core 2 configuration file. - Those using the Log4j 1 configuration compatibility layer with
org.apache.log4j.xml.XMLLayoutspecified 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, and specifically the section on eliminating reliance on the bridge.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Java / Kotlin (Maven) | org.apache.logging.log4j:log4j-1.2-api | >= 2.7, < 2.25.4, >= 3.0.0-beta1, <= 3.0.0-beta2 | 2.25.4 |
References
- https://nvd.nist.gov/vuln/detail/CVE-2026-34479
- https://github.com/apache/logging-log4j2/pull/4078
- https://github.com/apache/logging-log4j2
- 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
- CVSS 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- Weakness (CWE)
CWE-116- Platform
- Java / Kotlin (Maven)
- Package
org.apache.logging.log4j:log4j-1.2-api- Disclosed
- 10.04.2026
- Updated
- 11.10.2026 13:20
Sources and licenses
OSV / GitHub Advisory Database - GHSA-h383-gmxw-35v2 - CC BY 4.0
Vulnerability history: org.apache.logging.log4j:log4j-1.2-api
All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
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