How severe is CVE-2026-34479?

CVE-2026-34479 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-34479 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (41st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-34479?

CVE-2026-34479 primarily affects Apache Log4j. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-34479?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-34479 have an EU (EUVD) identifier?

Yes. CVE-2026-34479 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-21409.

When was CVE-2026-34479 published?

CVE-2026-34479 was published on 2026-04-10 and last updated on 2026-06-17.

CVE-2026-34479

CVE-2026-34479 is a high-severity vulnerability in Apache Log4j with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-116.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 6.9
EPSS exploit prediction: 1% (41st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-21409
Weakness: CWE-116
Affected product: Apache Log4j
Published: 2026-04-10
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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. 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.
How severe is CVE-2026-34479?: CVE-2026-34479 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-34479 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (41st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-34479?: CVE-2026-34479 primarily affects Apache Log4j. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-34479?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-34479 have an EU (EUVD) identifier?: Yes. CVE-2026-34479 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-21409.
When was CVE-2026-34479 published?: CVE-2026-34479 was published on 2026-04-10 and last updated on 2026-06-17.

References

Affected products (6)

cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*
cpe:2.3:a:apache:log4j:3.0.0:alpha1:*:*:*:*:*:*
cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc1:*:*:*:*:*:*
cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc2:*:*:*:*:*:*
cpe:2.3:a:apache:log4j:3.0.0:beta1:*:*:*:*:*:*
cpe:2.3:a:apache:log4j:3.0.0:beta2:*:*:*:*:*:*

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