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.
Affected products
apache: log4cxx
References6
- lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b Mailing ListVendor Advisory
- logging.apache.org/security.html#CVE-2026-40023 Vendor Advisory
- github.com/apache/logging-log4cxx/pull/609 Issue TrackingPatch
- logging.apache.org/cyclonedx/vdr.xml Product
- logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayo… Product
- www.openwall.com/lists/oss-security/2026/04/10/12 Mailing ListThird Party Advisory
Metrics
- CVSS 3.1
-
5.3
MEDIUM
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - CVSS 4.0
-
6.3
MEDIUM
Score source: CNA
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 1% percentile: 45 · as of 12 November 2026
- CWE
- CWE-116
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