Improper Output Neutralization for Logs Affecting org.apache.logging.log4j:log4j-core package, versions [2.21.0, 2.25.4)[3.0.0-beta1,]
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published10 Apr 2026
- disclosed10 Apr 2026
- creditSamuli Leinonen
Introduced: 10 Apr 2026
CVE-2026-34478 (opens in a new tab)How to fix?
A fix was pushed into the master branch but not yet published.
Overview
org.apache.logging.log4j:log4j-core is a logging library for Java.
Affected versions of this package are vulnerable to Improper Output Neutralization for Logs in the Rfc5424Layout plugin due to newLineEscape and useTlsMessageFormat configuration attributes being silently renamed, leading to improper handling of newline escaping for TCP framing and incorrect message formatting for TLS framing. An attacker can inject arbitrary log entries by supplying crafted CRLF sequences in log messages, potentially manipulating log output or bypassing log-based security controls.
Note:
This is only exploitable if the Rfc5424Layout is configured directly with affected attributes in stream-based syslog services.
Users of the SyslogAppender are not affected, as its configuration attributes were not modified.