Medium 6.9Published Apr 10, 2026

CVE-2026-34479Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters

Updated under an hour ago (Oct 27, 2026, 9:23 AM ET)

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It affects Apache Software Foundation Apache Log4j 1 to Log4j 2 bridge and 1 other product. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for Apache Software Foundation Apache Log4j 1 to Log4j 2 bridge

Exploited in the last 30 days

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.

CVSS: 6.9 MEDIUM (v4.0, CNA)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
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: apache
NVD analysis: Analyzed
Record last updated: Apr 10, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Apache Software Foundation Apache Log4j 1 to Log4j 2 bridge apache:log4j_1_2_api	from 2.7 before 2.25.4; from 3.0.0-alpha1 through 3.0.0-beta2	CNA record
apache log4j apache:log4j	from 2.7 before 2.25.4; 3.0.0; 3.0.0; 3.0.0; 3.0.0; 3.0.0	NVD

References

References

https://github.com/apache/logging-log4j2/pull/4078	patch, exploit, issue-tracking
https://logging.apache.org/security.html#CVE-2026-34479	vendor-advisory
https://logging.apache.org/cyclonedx/vdr.xml	vendor-advisory
https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html	related, mitigation
https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on	vendor-advisory, mailing-list
http://www.openwall.com/lists/oss-security/2026/04/10/8	mailing-list

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.