Apache Log4j Core verifyHostName TLS hostname verification bypass
CVE-2026-34477 is a hostname verification flaw in Apache Log4j Core caused by an incomplete fix for CVE-2025-68161. The prior fix only enforced hostname verification when enabled through the log4j2.sslVerifyHostName system property, but did not correctly handle the verifyHostName attribute configured on a nested <Ssl> element. As a result, the verifyHostName configuration attribute, introduced in Log4j Core 2.12.0, was silently ignored in affected versions through 2.25.3, and also in 3.0.0-alpha1 through 3.0.0-beta3. This leaves TLS connections established by affected network appenders vulnerable to improper certificate hostname validation even when administrators explicitly configured hostname verification. The issue affects SMTP, Socket, and Syslog appenders using TLS via a nested <Ssl> element. Apache stated that the HTTP appender is not affected because it uses a separate verifyHostName setting that was not subject to this bug and verifies hostnames by default.
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<Ssl> element in vulnerable Log4j Core versions. Exposure is also reduced where attackers cannot obtain or present a certificate chaining to a CA trusted by the relevant trust store. The HTTP appender is not affected by this specific flaw because it uses separate hostname verification logic and verifies hostnames by default. No complete workaround equivalent to the vendor fix was provided.Remediation
Patch, then assume compromise.
verifyHostName attribute in nested <Ssl> TLS configuration. Affected users include Log4j Core 2.12.0 through 2.25.3 and 3.0.0-alpha1 through 3.0.0-beta3.Exploits
No valid public exploits. Mallory filtered out 1 candidate as fakes, detection scripts, or README-only repos.
All candidate exploits were filtered out by Mallory's validation.
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Recent activity
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
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