Is CVE-2026-34478 being actively exploited?

It is not currently in CISA's KEV catalog. Its EPSS exploitation probability is 1%.

What products does CVE-2026-34478 affect?

Tracked products affected include Apache Log4j. Check the version you run to see whether it is affected.

How do I fix CVE-2026-34478?

Apply the vendor fix promptly. An official patch or advisory is available. Upgrade affected products to a fixed version.

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CVE-2026-34478

Q: What is CVE-2026-34478?

CVE-2026-34478 is a high-severity software vulnerability (CWE-117) with a CVSS score of 7.5. Apache Log4j Core's Rfc5424Layout https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout , in versions 2.21.0 through 2.25.3, is vulnerable to log injection via CRLF sequences due to undocumented renames of security-relevan

HIGH severity · CVSS 7.5 · CWE-117

7.5CVSS HIGH

Summary

Apache Log4j Core's Rfc5424Layout https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout , in versions 2.21.0 through 2.25.3, is vulnerable to log injection via CRLF sequences due to undocumented renames of security-relevant configuration attributes. Two distinct issues affect users of stream-based syslog services who configure Rfc5424Layout directly: * The newLineEscape attribute was silently renamed, causing newline escaping to stop working for users of TCP framing (RFC 6587), exposing them to CRLF injection in log output. * The useTlsMessageFormat attribute was silently renamed, causing users of TLS framing (RFC 5425) to be silently downgraded to unframed TCP (RFC 6587), without newline escaping. Users of the SyslogAppender are not affected, as its configuration attributes were not modified. Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue.

Impact & exploitability

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

Confidentiality impactNone

Integrity impactHigh

Availability impactNone

Exploit probability (EPSS)1%

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products we track (1)

Apache Log4j

Recommendation

Apply the vendor fix promptly. Open any affected product above for its exact safe version.

Official patch: https://github.com/apache/logging-log4j2/pull/4074 ↗

CVE-2026-34478

Summary

Impact & exploitability

Affected products we track (1)

Recommendation

Additional information