CVE-2026-40023
MediumCVSS 5.3Exploitation Probability (EPSS)
Low risk43th percentile - higher than 43% of all known CVEs
Summary
Apache Log4cxx before 1.7.0 (XMLLayout) fails to sanitize characters forbidden by the XML 1.0 specification in log messages and NDC/MDC property keys and values, producing invalid XML. Conforming XML parsers 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 suppress individual log records, impairing audit trails.
Risk Assessment
An attacker could suppress log records, hindering detection of malicious activity and weakening audit trails. This may lead to missed security incidents.
Recommendation
Upgrade Apache Log4cxx to version 1.7.0, which fixes the issue. Verify XMLLayout configuration and monitor log integrity.
Related vulnerabilities
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

