CVE-2026-34477: org.apache.logging.log4j:log4j-core:jar:2.25.3:compile

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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 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 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.

CVE: CVE-2026-34477
CWE: CWE-295

References

• https://guide.sonatype.com/vulnerability/CVE-2026-34477?component-type=maven&component-name=org.apache.logging.log4j%2Flog4j-core&utm_source=ossindex-client&utm_medium=integration&utm_content=1.8.1
• http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2026-34477
• Align SslConfiguration factory method usage with Log4j 2.12+ API apache/logging-log4j2#4075
• https://lists.apache.org/thread/lkx8cl46t2bvkcwfcb2pd43ygc097lq4
• GHSA-6hg6-v5c8-fphq