CVE-2026-40023

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.

• CWE-116

• https://github.com/apache/logging-log4cxx/pull/609Issue Tracking, Patch
• https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8bMailing List, Vendor Advisory
• https://logging.apache.org/cyclonedx/vdr.xmlProduct
• https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.htmlProduct
• https://logging.apache.org/security.html#CVE-2026-40023Vendor Advisory
• http://www.openwall.com/lists/oss-security/2026/04/10/12Mailing List, Third Party Advisory

Published

Apr 10, 2026

Last Modified

Jun 17, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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