Medium 6.9Published Apr 10, 2026

CVE-2026-34480Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters

Updated under an hour ago (Oct 27, 2026, 6:50 PM ET)

Does this affect you?

It affects Apache Software Foundation Apache Log4j Core. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

Do this next

Start free and add your stack

Free account, 1 product

Every CVE for Apache Software Foundation Apache Log4j Core

Exploited in the last 30 days

Apache Log4j Core's XmlLayout https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout , in versions up to and including 2.25.3, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets producing invalid XML output whenever a log message or MDC value contains such characters. The impact depends on the StAX implementation in use: * JRE built-in StAX: Forbidden characters are silently written to the output, producing malformed XML. Conforming parsers must reject such documents with a fatal error, which may cause downstream log-processing systems to drop the affected records. * Alternative StAX implementations (e.g., Woodstox https://github.com/FasterXML/woodstox , a transitive dependency of the Jackson XML Dataformat module): An exception is thrown during the logging call, and the log event is never delivered to its intended appender, only to Log4j's internal status logger. Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output.

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 Core apache:log4j	from 2.0-alpha1 before 2.25.4; from 3.0.0-alpha1 through 3.0.0-beta3	CNA record
apache log4j apache:log4j	from 2.0 before 2.25.4; 3.0.0; 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/4077	patch, issue-tracking
https://logging.apache.org/security.html#CVE-2026-34480	vendor-advisory
https://logging.apache.org/cyclonedx/vdr.xml	vendor-advisory, product
https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout	related, technical-description
https://lists.apache.org/thread/5x0hcnng0chhghp6jgjdp3qmbbhfjzhb	vendor-advisory, mailing-list
http://www.openwall.com/lists/oss-security/2026/04/10/9	mailing-list, third-party-advisory

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.