CVE-2026-40023
An attacker who can influence logged data can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity.
Does this matter?
Lower severity and a low EPSS score (0.50%). Track it; it rarely justifies an emergency change on its own.
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 4.0
- 6.3 MEDIUMCVSS: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/M
- EPSS
- 0.50% probability · 42th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-116
- Affected
- apache/log4cxx
- Source
- security@apache.org
EPSS 0.5% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://github.com/apache/logging-log4cxx/pull/609Issue Tracking, Patch
- https://lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8bMailing List, Vendor 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 List, Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.