CVE-2026-40023

Apache Log4cxx, Apache Log4cxx (Conan), Apache Log4cxx (Brew): Silent log event loss in XMLLayout due to unescaped XML 1.0 forbidden characters

CVSS 6.3 MEDIUMEPSS 0.5%CWE-116

Vexday Risk Score

13Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 6.3EPSS 0.5%KEV nãoPoC —Nuclei —Metasploit —Patch referenciado

Lifecycle

10 Apr 2026Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

Apache Log4cxx's XMLLayout https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html , in versions before 1.7.0, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets in log messages, NDC, and MDC property keys and values, producing invalid XML output. Conforming XML parsers must reject such documents with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records. An attacker who can influence logged data can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity. Users are advised to upgrade to Apache Log4cxx 1.7.0, which fixes this issue.

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Affected products

Apache Software Foundation · Apache Log4cxx Apache Software Foundation · Apache Log4cxx (Brew)Apache Software Foundation · Apache Log4cxx (Conan)

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References

https://github.com/apache/logging-log4cxx/pull/609 https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b https://logging.apache.org/cyclonedx/vdr.xml https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html https://logging.apache.org/security.html#CVE-2026-40023 http://www.openwall.com/lists/oss-security/2026/04/10/12