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.
Fix
Patch, vendor advisory and mitigation references on NVD 3
- https://github.com/apache/logging-log4cxx/pull/609 Issue Tracking, Patch
- https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b Mailing List, Vendor Advisory
- https://logging.apache.org/security.html#CVE-2026-40023 Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 6.3 · apacheNVD modified 2026-10-26 21:10
Affected (CPE criteria) 1
cpe:2.3:a:apache:log4cxx:*:*:*:*:*:*:*:*
References 6
- https://github.com/apache/logging-log4cxx/pull/609 Issue Tracking, Patch
- https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b Mailing List, Vendor Advisory
- https://logging.apache.org/cyclonedx/vdr.xml Product
- https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html Product
- https://logging.apache.org/security.html#CVE-2026-40023 Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/04/10/12 Mailing List, Third Party Advisory