CVE-2026-344806.9MediumCWE-116

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

Apache Software Foundation · Apache Log4j Core

Vendor fix available · Affected: Apache Software Foundation Apache Log4j Core · Exploitation: possible (1 to 10%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

1.1%probability of exploitation in the next 30 days

65th percentile

050100

Higher than 65% of scored CVEs

6.9MediumCVSS 4.0

LowMediumHighCrit.

DescriptionCVE.org

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.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

Apache Software Foundation · Apache Log4j Corefrom 2.0-alpha1 before 2.25.4; from 3.0.0-alpha1 up to and including 3.0.0-beta3

On the Atlas

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Open the Atlas

Exploitation: Possible (1 to 10%). EPSS between 1% and 10%.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Improper Encoding or Escaping of Output · Injection and Smuggling
Vendor: Apache Software Foundation
Published: April 2026
Band: Possible (1 to 10%), April 2026

CoverageNo articles yet

No CyberSIXT article names CVE-2026-34480 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.