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Java EUVDEUVD-2026-21407

| CVE-2026-34477 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 · Vendor: apache
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Vulnerability Assessment

Weakness
CWE
CWE-297
OWASP Top 10:2025
A07:2025 - Authentication Failures
ASVS 5.0
V12 - Secure Communication Certificate host validation
Impact

The CVSS 4.0 vector (AV:N/AC:H/AT:N/PR:N/UI:N with VC:L/SI:L) reflects network attack vector with high complexity, resulting in low confidentiality and integrity impact-appropriate for a man-in-the-middle scenario requiring both attacker network position and a valid certificate from a trusted CA. EPSS data is not provided, but real-world risk depends critically on deployment specifics: organizations using SMTP, Socket, or Syslog appenders over untrusted networks with the verifyHostName attribute explicitly configured face genuine risk, as they have clearly signaled security intent that was silently defeated. However, the high attack complexity (AC:H) due to certificate requirements and the conditional nature (specific appender types, specific configuration) limits the overall threat landscape. This is not a pre-authentication remote code execution scenario but rather a configuration bypass that undermines transport security for logging data. Organizations that never configured verifyHostName are unaffected; those that did face unexpected vulnerability despite explicit configuration.
Exploit ScenarioDerived

An attacker positioned on the network path between a Log4j-based application and its logging destination (e.g., a remote Syslog server) intercepts the connection. The attacker presents a TLS certificate issued by a certificate authority trusted by the application's JVM (such as a public CA or internal enterprise CA). Because the verifyHostName attribute in the <Ssl> configuration was silently ignored, the Log4j appender accepts the attacker's certificate despite the hostname mismatch, allowing the attacker to decrypt, read, and potentially modify log messages in transit. This requires the application to have explicitly configured the verifyHostName attribute (indicating security intent) and use SMTP, Socket, or Syslog appenders with TLS. No public exploit code is required-the vulnerability is in the silent non-enforcement of existing configuration.
This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.1% exploitation probability (EPSS)

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AnalysisAIv1 – Apr 10, 2026

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.

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.

Affected VersionsENISA

Apache Log4j Core 2.12.0 <2.25.4
Apache Log4j Core 3.0.0-alpha1 ≤3.0.0-beta3

Affected Packages

maven org.apache.logging.log4j:log4j-core fix: 2.25.4
euvd apache_log4j_core fix: 2.25.4

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 2 packages in maven, euvd

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Technical ContextAI · show details

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.

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Severity by source

Vendor (apache) 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
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

Primary rating from Vendor (apache).

CVSS VectorVendor: apache

Attack Vector
Network
Attack Complexity
High
Attack Requirements
None
Privileges Required
None
User Interaction
None
Vulnerable system: Confidentiality
Low
Vulnerable system: Integrity
None
Vulnerable system: Availability
None
Subsequent system: Confidentiality
None
Subsequent system: Integrity
Low
Subsequent system: Availability
None

Lifecycle Timeline

2
Patch released
Apr 10, 2026 - 16:00 nvd
Patch available
CVE Published
Apr 10, 2026 - 15:36 nvd
MEDIUM 6.3

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.

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.

Threat Intelligence Overview

EPSS Score
0.1%
Top 71% exploitable
Exploit
POC
Public exploit code exists
Social Media
1
Sightings
Data Quality
8 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment Vendor CIRCL GitHub VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC Yes
EPSS 0.1%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
No
Human Impact· derived
Medium
Technical Impact
Partial

Priority Score

52
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +32
PoC: +20
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

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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

References

Advisories & patches
PATCH https://github.com/apache/logging-log4j2/pull/4075 ADVISORY https://lists.apache.org/thread/lkx8cl46t2bvkcwfcb2pd43ygc097lq4 ADVISORY https://logging.apache.org/cyclonedx/vdr.xml ADVISORY https://logging.apache.org/security.html#CVE-2026-34477 ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-34477 ADVISORY https://vuldb.com/vuln/356842 ADVISORY https://www.herodevs.com/vulnerability-directory/cve-2026-34477 REF https://logging.apache.org/log4j/2.x/manual/appenders/network.html#SslConfiguration-attr-verifyHostName

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