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CVE-2026-34479

Apache Log4j vulnerability

7.5 HIGHPublic exploitEPSS 0.91%
  1. Published10 Apr 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products

Apache Log4j≥ 2.7 < 2.25.4 · 3.0.0

Remediation

Fixed in
Apache Log4j≥ 2.25.4

References

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Frequently asked

Is CVE-2026-34479 being actively exploited?

CVE-2026-34479 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.91%.

How severe is CVE-2026-34479?

CVE-2026-34479 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.91% probability of exploitation.

Which products are affected by CVE-2026-34479?

Affected products include Apache Log4j.

How do I fix CVE-2026-34479?

Upgrade affected software to a fixed version, for example Apache Log4j 2.25.4 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.