Vulnerability 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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Apache | Log4Cxx | < 1.7.0 |
Related Weaknesses (CWE)
References
- https://github.com/apache/logging-log4cxx/pull/609Issue TrackingPatch
- https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8bMailing ListVendor 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 ListThird Party Advisory
FAQ
What is CVE-2026-40023?
CVE-2026-40023 is a vulnerability with a CVSS score of 5.3 (MEDIUM). 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 specificat...
How severe is CVE-2026-40023?
CVE-2026-40023 has been rated MEDIUM with a CVSS base score of 5.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-40023?
Check the references section above for vendor advisories and patch information. Affected products include: Apache Log4Cxx.