CVE-2026-34479Medium▾ SunlitApache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters
▾ Sunlit zone — Low / medium · no exploitation signal
impact 27.5 · likelihood 0.1 · exploitation 0
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Exploit-prediction probability, daily snapshots since Oct 26.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via GHSA
Last analysed / modified upstream
0.5%
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:
Log4j1XmlLayout directly in a Log4j Core 2 configuration file.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, and specifically the section on eliminating reliance on the bridge.
org.apache.logging.log4j:log4j-core >= 2.7, < 2.25.4org.apache.logging.log4j:log4j-core >= 3.0.0-beta1, <= 3.0.0-beta2Upgrade to a patched release:
org.apache.logging.log4j:log4j-core 2.25.4Connected by shared product, vendor, weakness, or advisory.
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