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Java CVE-2026-34477

| EUVDEUVD-2026-21407 MEDIUM
Improper Validation of Certificate with Host Mismatch (CWE-297)
2026-04-10 apache GHSA-6hg6-v5c8-fphq
Apache Java Information Disclosure Apache Log4J Core Apache Software Foundation
6.3
CVSS 4.0 · NVD
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Severity by source

NVD PRIMARY
6.3 MEDIUM
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
SUSE
6.5 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
Red Hat
6.8 MEDIUM
qualitative

Primary rating from NVD.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

4
EUVD ID Assigned
Apr 10, 2026 - 16:00 euvd
EUVD-2026-21407
Analysis Generated
Apr 10, 2026 - 16:00 vuln.today
Patch released
Apr 10, 2026 - 16:00 nvd
Patch available
CVE Published
Apr 10, 2026 - 15:36 nvd
MEDIUM 6.3

Blast Radius

ecosystem impact
† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth
  • 695 maven packages depend on org.apache.logging.log4j:log4j-core (150 direct, 548 indirect)

Ecosystem-wide dependent count for version 2.12.0.

DescriptionCVE.org

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.

AnalysisAI

Man-in-the-middle attacks are possible in Apache Log4j Core through 2.25.3 when SMTP, Socket, or Syslog appenders use TLS with the verifyHostName attribute configured in the <Ssl> element, because the attribute was silently ignored despite being available since version 2.12.0. This is a regression from an incomplete fix to CVE-2025-68161 that only addressed hostname verification via system property. An attacker with a certificate from a trusted CA can intercept TLS connections. Apache has released patched version 2.25.4 to correct this issue.

Technical ContextAI

Log4j Core's network appenders (SMTP, Socket, Syslog) support TLS encryption via nested <Ssl> configuration elements. The verifyHostName attribute, introduced in Log4j 2.12.0, is intended to validate that the server certificate's hostname matches the target hostname, a critical defense against man-in-the-middle attacks under CWE-297 (Improper Certificate Validation). The root cause is that this configuration attribute was parsed but never actually enforced during TLS handshakes across all versions through 2.25.3. The HTTP appender uses a separate verifyHostname attribute (with different capitalization) that was properly implemented and is not affected. This represents a configuration validation gap where user intent was not translated into runtime security behavior.

RemediationAI

Vendor-released patch: Apache Log4j Core 2.25.4 or later. Immediately upgrade to version 2.25.4, which corrects the verifyHostName attribute enforcement in <Ssl> configuration elements for SMTP, Socket, and Syslog appenders. As an interim mitigation, organizations may enable hostname verification via the log4j2.sslVerifyHostName system property instead of the <Ssl> element attribute, as the previous incomplete fix for CVE-2025-68161 did address the system property path. However, this is not a complete workaround and upgrading is the recommended remediation. See Apache advisory at https://logging.apache.org/security.html#CVE-2026-34477 and patch pull request at https://github.com/apache/logging-log4j2/pull/4075.

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Vendor StatusVendor

SUSE

Severity: Medium
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise Module for Basesystem 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Server for SAP Applications 15 SP7 Affected

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CVE-2026-34477 vulnerability details – vuln.today
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