Apache Log4J Core
Monthly
Apache Log4j Core's XmlLayout in versions up to 2.25.3 fails to sanitize XML-forbidden characters, producing malformed XML output when log messages or MDC values contain such characters. The impact varies by StAX implementation: JRE's built-in StAX silently writes invalid XML that conforming parsers reject, potentially causing downstream log-processing systems to drop records; alternative StAX implementations like Woodstox throw exceptions during logging calls, preventing event delivery to the intended appender. No public exploit code or active exploitation has been identified; this is a data integrity and log availability issue rather than a confidentiality or authentication bypass. Patch version 2.25.4 is available from Apache.
Apache Log4j Core 2.21.0 through 2.25.3 allows remote log injection via CRLF sequences in Rfc5424Layout due to undocumented renaming of security-relevant configuration attributes (newLineEscape and useTlsMessageFormat). Attackers can inject malicious log entries or downgrade TLS-framed syslog to unframed TCP, compromising log integrity for stream-based syslog services. SyslogAppender users are not affected. CVSS 6.9 indicates medium-to-high severity; EPSS and exploitation signals not available at time of analysis.
Man-in-the-middle attacks are possible in Apache Log4j Core through 2.25.3 when SMTP, Socket, or Syslog appenders use TLS with the verifyHostName attribute configured in the <Ssl> element, because the attribute was silently ignored despite being available since version 2.12.0. This is a regression from an incomplete fix to CVE-2025-68161 that only addressed hostname verification via system property. An attacker with a certificate from a trusted CA can intercept TLS connections. Apache has released patched version 2.25.4 to correct this issue.
Apache Log4j Core's XmlLayout in versions up to 2.25.3 fails to sanitize XML-forbidden characters, producing malformed XML output when log messages or MDC values contain such characters. The impact varies by StAX implementation: JRE's built-in StAX silently writes invalid XML that conforming parsers reject, potentially causing downstream log-processing systems to drop records; alternative StAX implementations like Woodstox throw exceptions during logging calls, preventing event delivery to the intended appender. No public exploit code or active exploitation has been identified; this is a data integrity and log availability issue rather than a confidentiality or authentication bypass. Patch version 2.25.4 is available from Apache.
Apache Log4j Core 2.21.0 through 2.25.3 allows remote log injection via CRLF sequences in Rfc5424Layout due to undocumented renaming of security-relevant configuration attributes (newLineEscape and useTlsMessageFormat). Attackers can inject malicious log entries or downgrade TLS-framed syslog to unframed TCP, compromising log integrity for stream-based syslog services. SyslogAppender users are not affected. CVSS 6.9 indicates medium-to-high severity; EPSS and exploitation signals not available at time of analysis.
Man-in-the-middle attacks are possible in Apache Log4j Core through 2.25.3 when SMTP, Socket, or Syslog appenders use TLS with the verifyHostName attribute configured in the <Ssl> element, because the attribute was silently ignored despite being available since version 2.12.0. This is a regression from an incomplete fix to CVE-2025-68161 that only addressed hostname verification via system property. An attacker with a certificate from a trusted CA can intercept TLS connections. Apache has released patched version 2.25.4 to correct this issue.