CVE-2026-34479: CWE-116 Improper Encoding or Escaping of Output in Apache Software Foundation Apache Log4j 1 to Log4j 2 bridge
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.
AI Analysis
Technical Summary
The Apache Log4j 1-to-Log4j 2 bridge's Log4j1XmlLayout does not escape characters forbidden by the XML 1.0 standard, producing malformed XML output. XML parsers that conform to the standard will reject such malformed documents with fatal errors, which can cause downstream log processing systems to drop or fail to index these log entries. This affects users who configure Log4j Core 2 with Log4j1XmlLayout or use the Log4j 1 compatibility layer specifying org.apache.log4j.xml.XMLLayout. The bridge is deprecated and will be removed in Log4j 3. Users should upgrade to version 2.25.4 of the bridge, which corrects this issue, and consult the migration guide to remove dependency on the bridge.
Potential Impact
Malformed XML output caused by improper escaping can lead to fatal errors in XML parsers used by downstream log processing systems. This may result in loss or failure to index log records, potentially impacting log integrity and monitoring capabilities. There is no indication of remote code execution or privilege escalation. No known exploits are reported in the wild.
Mitigation Recommendations
Users should upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which fixes the improper escaping issue. Additionally, since the bridge is deprecated and will not be included in Log4j 3, users are advised to consult the official migration guide to eliminate reliance on the bridge. Patch status is not explicitly stated in the advisory fields, but the description clearly states that version 2.25.4 corrects the issue.
CVE-2026-34479: CWE-116 Improper Encoding or Escaping of Output in Apache Software Foundation Apache Log4j 1 to Log4j 2 bridge
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.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The Apache Log4j 1-to-Log4j 2 bridge's Log4j1XmlLayout does not escape characters forbidden by the XML 1.0 standard, producing malformed XML output. XML parsers that conform to the standard will reject such malformed documents with fatal errors, which can cause downstream log processing systems to drop or fail to index these log entries. This affects users who configure Log4j Core 2 with Log4j1XmlLayout or use the Log4j 1 compatibility layer specifying org.apache.log4j.xml.XMLLayout. The bridge is deprecated and will be removed in Log4j 3. Users should upgrade to version 2.25.4 of the bridge, which corrects this issue, and consult the migration guide to remove dependency on the bridge.
Potential Impact
Malformed XML output caused by improper escaping can lead to fatal errors in XML parsers used by downstream log processing systems. This may result in loss or failure to index log records, potentially impacting log integrity and monitoring capabilities. There is no indication of remote code execution or privilege escalation. No known exploits are reported in the wild.
Mitigation Recommendations
Users should upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which fixes the improper escaping issue. Additionally, since the bridge is deprecated and will not be included in Log4j 3, users are advised to consult the official migration guide to eliminate reliance on the bridge. Patch status is not explicitly stated in the advisory fields, but the description clearly states that version 2.25.4 corrects the issue.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- apache
- Date Reserved
- 2026-03-28T14:06:31.965Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69d91fde1cc7ad14dacba282
Added to database: 4/10/2026, 4:05:50 PM
Last enriched: 4/10/2026, 4:21:25 PM
Last updated: 4/11/2026, 5:15:57 AM
Views: 5
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