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Vulnerabilities

Vulnerability · CVE-2026-34479

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.

Published Apr 10, 2026 · catalog updated Jun 17, 2026 · Apache

Check if you run it

No confirmed exploitation is on record for CVE-2026-34479. EPSS is 0.91%. Act only if a listed version of Apache is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.9
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.91%
Remediation
Advisory link
Affected products
cpe apache/log4j

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe apache/log4j3.0.0

How to fix CVE-2026-34479

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-34479. EPSS is 0.91%. Act only if a listed version of Apache is installed.

Which versions are affected?

Compare what you have installed with 3.0.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-116. EPSS 0.91%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jun 17, 2026 · NIST NVD

    Updated

    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

  2. Oct 15, 2026 · Apache Software Foundation

    Detected

    Named on the public Apache Software Foundation page.

Sources

  • Apache Software FoundationVendor advisoryCVE-2026-34479

    CVE-2026-34479 is named on the public Apache Software Foundation page.

    logging.apache.org
  • CVE.orgVulnerability recordCVE-2026-34479

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-34479

    30-day exploitation probability 0.9%

    first.org
  • NIST NVDVulnerability recordCVE-2026-34479

    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 downs

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.