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Fencer Vulns
high 7.5

CVE-2026-34480 json

Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters

published 2026-04-10 6 mo ago modified 2026-10-26 13 d ago also GHSA-3pxv-7cmr-fjr4 , EUVD-2026-21410

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 64%
public exploits
0
none known

Summary

Apache Log4j Core's XmlLayout https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout , in versions up to and including 2.25.3, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets producing invalid XML output whenever a log message or MDC value contains such characters.

The impact depends on the StAX implementation in use:

* JRE built-in StAX: Forbidden characters are silently written to the output, producing malformed XML. Conforming parsers must reject such documents with a fatal error, which may cause downstream log-processing systems to drop the affected records. * Alternative StAX implementations (e.g., Woodstox https://github.com/FasterXML/woodstox , a transitive dependency of the Jackson XML Dataformat module): An exception is thrown during the logging call, and the log event is never delivered to its intended appender, only to Log4j's internal status logger.

Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output.

Patch / fix

  • maven org.apache.logging.log4j:log4j-core 2.25.4
  • Apache Software Foundation Apache Log4j Core 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-2026-34480 updated cvss 5.3

org.apache.logging.log4j/log4j-core: Apache Log4j Core: Invalid XML output causes denial of service in logging

  • Red Hat AI Inference Server redhat-user-workloads/ai-tenant/rhaiis-3-3/rhaiis-cuda-ubi9-3-3 Red Hat build of Apicurio Registry 2 log4j-core Red Hat build of Apicurio Registry 3 log4j-core
    affected: workaround, no fix planned “Will not fix”
  • Red Hat build of OptaPlanner 8 log4j-core
    affected: workaround, no fix available
  • Red Hat Enterprise Linux 9 log4j, log4j-jcl, log4j-slf4j
    affected: workaround, no fix planned “Will not fix”
  • Red Hat Enterprise Linux AI (RHEL AI) 3 bazel7, bazel8, rhelai3/bootc-cuda-rhel9, redhat-user-workloads/rhel-ai-tenant/rhelai-bootc-3-3/bootc-cuda-aws-3-3, redhat-user-workloads/rhel-ai-tenant/rhelai-bootc-3-3/bootc-cuda-gcp-3-3, redhat-user-workloads/rhel-ai-tenant/rhelai-bootc-3-3/bootc-cuda-azure-3-3
    affected: workaround, no fix available
  • Red Hat Fuse 7 log4j-core Red Hat JBoss Enterprise Application Platform 7 log4j-core
    affected: workaround, no fix planned “Will not fix”
  • Red Hat Offline Knowledge Portal redhat-user-workloads/rhocc-mimir-tenant/mimir/rhokp-core-encrypted
    affected: workaround, no fix available
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-pipeline-runtime-pytorch-cuda-py312-rhel9, rhoai/odh-pipeline-runtime-pytorch-rocm-py312-rhel9, rhoai/odh-workbench-jupyter-pytorch-cuda-py312-rhel9, rhoai/odh-workbench-jupyter-pytorch-rocm-py312-rhel9, rhoai/odh-workbench-jupyter-trustyai-cpu-py312-rhel9, rhoai/odh-pipeline-runtime-datascience-cpu-py312-rhel9, +5 more
    affected: workaround, no fix planned “Will not fix”
  • Red Hat HawtIO HawtIO 4.4.0
    fixed: vendor fix RHSA-2026:25089
show 13 more
  • Red Hat AMQ Broker 7.13.6
    fixed: vendor fix RHSA-2026:66545
  • Red Hat AMQ Broker 7.14.1
    fixed: vendor fix RHSA-2026:66488
  • Red Hat build of Apache Camel 4.18.1.P1 for Spring Boot 3.5.16
    fixed: vendor fix RHSA-2026:37390
  • Red Hat Data Grid 8.6.1
    fixed: vendor fix RHSA-2026:22619
  • Red Hat Offline Knowledge Portal 1.2.13 offline-knowledge-portal/rhokp-rhel9 1779996999
    fixed: vendor fix RHSA-2026:21773
  • Red Hat OpenShift AI 2.25 rhoai/odh-modelmesh-rhel9 1783443816
    fixed: vendor fix RHSA-2026:42644
  • Red Hat Streams for Apache Kafka 2.9.4
    fixed: vendor fix RHSA-2026:34608
  • Red Hat Streams for Apache Kafka 3.2.1
    fixed: vendor fix RHSA-2026:54435
  • Red Hat AI Inference Server redhat-user-workloads/ai-tenant/rhaiis-3-2-2/rhaiis-cuda-ubi9-3-2-2 Red Hat Enterprise Linux 8 log4j, resteasy, log4j-jcl, log4j-web, log4j-slf4j, resteasy-javadoc
    not affected: vulnerable code not present
  • Red Hat Enterprise Linux 9 resteasy, pki-resteasy-core, pki-resteasy-client, pki-resteasy-jackson2-provider, pki-resteasy-servlet-initializer
    not affected: component not present
  • Red Hat JBoss Enterprise Application Platform 8 log4j-core, log4j-core-test Red Hat JBoss Enterprise Application Platform Expansion Pack log4j-core, log4j-core-test
    not affected: vulnerable code not present
  • Red Hat JBoss Web Server 6 log4j-core
    not affected: component not present
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-modelmesh-rhel8, rhoai/odh-vllm-cuda-rhel9, rhoai/odh-vllm-gaudi-rhel9 Red Hat OpenShift AI 2.25 rhoai/odh-rhel9-operator 1784004914, rhoai/odh-vllm-cpu-rhel9 1782397826, rhoai/odh-dashboard-rhel9 1782826282, rhoai/odh-operator-bundle 1784005555, rhoai/odh-vllm-cuda-rhel9 1783998774, rhoai/odh-vllm-rocm-rhel9 1783998857, +69 more
    not affected: vulnerable code not present

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

1.06% chance of exploitation in the next 30 days, higher than 64% of all scored CVEs (FIRST EPSS, 2026-11-08).

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
>=2.0-alpha1, <2.25.4
>=3.0.0-alpha1, <=3.0.0-beta3
2.25.4

Affected products

  • Apache Software Foundation Apache Log4j Core

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.