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Fencer Vulns
medium 5.9

CVE-2026-34477 json

Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration, allowing hostname verification bypass

published 2026-04-10 6 mo ago modified 2026-10-26 13 d ago also GHSA-6hg6-v5c8-fphq , EUVD-2026-21407

cvss
5.9
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 47%
public exploits
0
none known

Summary

The fix for CVE-2025-68161 https://logging.apache.org/security.html#CVE-2025-68161 was incomplete: it addressed hostname verification only when enabled via the log4j2.sslVerifyHostName https://logging.apache.org/log4j/2.x/manual/systemproperties.html#log4j2.sslVerifyHostName system property, but not when configured through the verifyHostName https://logging.apache.org/log4j/2.x/manual/appenders/network.html#SslConfiguration-attr-verifyHostName attribute of the <Ssl> element.

Although the verifyHostName configuration attribute was introduced in Log4j Core 2.12.0, it was silently ignored in all versions through 2.25.3, leaving TLS connections vulnerable to interception regardless of the configured value.

A network-based attacker may be able to perform a man-in-the-middle attack when all of the following conditions are met:

* An SMTP, Socket, or Syslog appender is in use. * TLS is configured via a nested <Ssl> element. * The attacker can present a certificate issued by a CA trusted by the appender's configured trust store, or by the default Java trust store if none is configured. This issue does not affect users of the HTTP appender, which uses a separate verifyHostname https://logging.apache.org/log4j/2.x/manual/appenders/network.html#HttpAppender-attr-verifyHostName attribute that was not subject to this bug and verifies host names by default.

Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue.

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-2026-34477 updated cvss 6.8

org.apache.logging.log4j/log4j-core: Apache Log4j Core: Man-in-the-middle attack due to incomplete hostname verification

  • Red Hat AI Inference Server redhat-user-workloads/ai-tenant/rhaiis-3-3/rhaiis-cuda-ubi9-3-3, redhat-user-workloads/ai-tenant/rhaiis-3-2-2/rhaiis-cuda-ubi9-3-2-2 Red Hat AMQ Broker 7 log4j-core Red Hat build of Apache Camel - HawtIO 4 log4j-core Red Hat build of Apache Camel for Spring Boot 4 log4j-core Red Hat build of Apicurio Registry 2 log4j-core Red Hat build of Apicurio Registry 3 log4j-core
    +3 more products
    Red Hat build of OptaPlanner 8 log4j-core Red Hat Data Grid 8 log4j-core, log4j-core-test Red Hat Enterprise Linux 8 log4j, resteasy, log4j-jcl, log4j-web, log4j-slf4j, resteasy-javadoc
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 9 log4j, resteasy, log4j-jcl, log4j-slf4j, pki-resteasy-core, pki-resteasy-client, +2 more
    affected: workaround, no fix available, no fix planned “Out of support scope”
  • 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 Red Hat Fuse 7 log4j-core Red Hat JBoss Enterprise Application Platform 7 log4j-core 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 Red Hat JBoss Web Server 6 log4j-core
    +4 more products
    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, rhoai/odh-vllm-cuda-rhel9, rhoai/odh-vllm-gaudi-rhel9, rhoai/odh-pipeline-runtime-pytorch-cuda-py312-rhel9, rhoai/odh-pipeline-runtime-pytorch-rocm-py312-rhel9, +9 more Red Hat streams for Apache Kafka 2 log4j-core Red Hat streams for Apache Kafka 3 log4j-core
    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
no
Technical impact
partial
Assessed
6 mo ago

Exploit prediction

0.57% chance of exploitation in the next 30 days, higher than 47% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:L/SA:N
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/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 5.9 CVSS:3.1/AV:N/AC:H/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
>=2.12.0, <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-297 Improper Validation of Certificate with Host Mismatch
  • CWE-295 Improper Certificate Validation
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.