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Fencer Vulns
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 2026-04-10 6 mo ago modified 2026-10-26 13 d ago also GHSA-h383-gmxw-35v2 , EUVD-2026-21409

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

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
6 mo ago

Exploit prediction

0.54% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-08).

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 Vulns 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.