Summary
Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration
The fix for CVE-2025-68161 was incomplete: it addressed hostname verification only when enabled via the log4j2.sslVerifyHostName system property, but not when configured through the 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 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 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.
Impact
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-34477? CVE-2026-34477 is a medium-severity security vulnerability in org.apache.logging.log4j:log4j-core (maven), affecting versions >= 2.12.0, < 2.25.4. It is fixed in 2.25.4.
- Which versions of org.apache.logging.log4j:log4j-core are affected by CVE-2026-34477? org.apache.logging.log4j:log4j-core (maven) versions >= 2.12.0, < 2.25.4 is affected.
- Is there a fix for CVE-2026-34477? Yes. CVE-2026-34477 is fixed in 2.25.4. Upgrade to this version or later.
- Is CVE-2026-34477 exploitable, and should I be worried? Whether CVE-2026-34477 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-34477 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-34477? Upgrade
org.apache.logging.log4j:log4j-coreto 2.25.4 or later.