CVE-2026-34479

Name	CVE-2026-34479
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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
apache-log4j1.2 (PTS)	bullseye	1.2.17-10+deb11u1	fixed
	bookworm, forky, sid, trixie	1.2.17-11	fixed
apache-log4j2 (PTS)	bullseye	2.17.1-1~deb11u1	vulnerable
	bullseye (security)	2.17.1-1~deb11u2	vulnerable
	bookworm, forky, sid, trixie	2.19.0-2	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
apache-log4j1.2	source	(unstable)	(not affected)
apache-log4j2	source	(unstable)	(unfixed)

Notes

- apache-log4j1.2 <not-affected> (Vulnerable code not present)
https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on
https://logging.apache.org/security.html#CVE-2026-34479
https://github.com/apache/logging-log4j2/pull/4078
Fixed by: https://github.com/apache/logging-log4j2/commit/25043cfad1bac2e43ebc4638450cbb73c51451c4 (rel/2.25.4)