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Fencer Intel
high 7.5

CVE-2026-34479 json

Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters

published 6mo ago modified 14d ago also EUVD-2026-21409 , GHSA-h383-gmxw-35v2

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 45%
public exploits
0
none known

Summary

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.

Patch / fix

  • maven org.apache.logging.log4j:log4j-core 2.25.4
  • Apache Software Foundation Apache Log4j 1 to Log4j 2 bridge 2.25.4
  • log4j openSUSE Tumbleweed 2.20.0-2.1

opensuse advisories openSUSE-SU-2026:10544-1

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-34479 updated cvss 5.3

org.apache.logging.log4j/log4j-1.2-api: Apache Log4j 1-to-Log4j 2 bridge: Log processing denial of service due to improper XML escaping

  • Red Hat Data Grid 8 log4j-1.2-api Red Hat Enterprise Linux 8 log4j, log4j-jcl, log4j-web, log4j-slf4j
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 9 log4j, log4j-jcl, log4j-slf4j
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Fuse 7 log4j-1.2-api Red Hat JBoss Enterprise Application Platform 7 log4j-1.2-api Red Hat JBoss Enterprise Application Platform 8 log4j-1.2-api Red Hat JBoss Enterprise Application Platform Expansion Pack log4j-1.2-api Red Hat Offline Knowledge Portal redhat-user-workloads/rhocc-mimir-tenant/mimir/rhokp-core-encrypted Red Hat OpenShift AI (RHOAI) rhoai/odh-modelmesh-rhel8, rhoai/odh-modelmesh-rhel9
    +1 more products
    Red Hat streams for Apache Kafka 3 log4j-1.2-api
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Offline Knowledge Portal 1.2.13 offline-knowledge-portal/rhokp-rhel9 1779996999
    fixed: vendor fix RHSA-2026:21773

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
6mo ago

Exploit prediction

0.54% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/apache/logging-log4j2/pull/4078 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 6.9 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
CNA 4.0 6.9 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
maven org.apache.logging.log4j:log4j-core
>=2.7, <2.25.4
>=3.0.0-beta1, <=3.0.0-beta2
2.25.4

Affected products

  • Apache Software Foundation Apache Log4j 1 to Log4j 2 bridge

Classification

Weakness
  • CWE-116 Improper Encoding or Escaping of Output
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.