CVE-2026-40023
Description
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.
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Affected products
2Patches
Vulnerability mechanics
References
6- github.com/apache/logging-log4cxx/pull/609nvdIssue TrackingPatch
- www.openwall.com/lists/oss-security/2026/04/10/12nvdMailing ListThird Party Advisory
- lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8bnvdMailing ListVendor Advisory
- logging.apache.org/security.htmlnvdVendor Advisory
- logging.apache.org/cyclonedx/vdr.xmlnvdProduct
- logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.htmlnvdProduct
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