Severity: moderate Affected versions:
- Apache Log4cxx before 1.7.0 - Apache Log4cxx (Conan) (log4cxx) before 1.7.0 - Apache Log4cxx (Brew) (log4cxx) before 1.7.0 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. Credit: Olawale Titiloye (finder) References: https://github.com/apache/logging-log4cxx/pull/609 https://logging.apache.org/security.html#CVE-2026-40023 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/ https://www.cve.org/CVERecord?id=CVE-2026-40023 Timeline: 2026-03-15: Vulnerability reported by Olawale Titiloye 2026-03-16: Fix shared publicly by Stephen Webb as pull request #609 2026-04-04: Log4cxx 1.7.0 released
