CVE Catalog

CVE-2026-34479

HighCVSS 7.5
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.54%

45th percentile - higher than 45% of all known CVEs

Summary

Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by XML 1.0, producing malformed XML. Conforming XML parsers reject such documents with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records.

Risk Assessment

Log processing systems may reject or fail to index records containing invalid characters, leading to loss of audit or diagnostic data. This affects users of Log4j1XmlLayout directly or the Log4j 1 compatibility layer with XMLLayout.

Recommendation

Update the Apache Log4j 1-to-Log4j 2 bridge to version 2.25.4, which fixes the issue. Consider migrating away from the bridge, which is deprecated and will not be present in Log4j 3.

Related vulnerabilities

Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS