Vulnerability in Apache Log4net
CVE-2026-40021
Apache Log4net's XmlLayout https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list and XmlLayoutSchemaLog4J https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list , in versions before 3…
EPSS: 0.007 (50.9th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.
Affected products
- Apache Log4net
- Apache Software Foundation Log4net — versions 0
Weakness classification (CWE)
References
- security@apache.org (patch, Issue Tracking)
- security@apache.org (vendor-advisory, Vendor Advisory)
- security@apache.org (Product, vendor-advisory)
- security@apache.org (related, Product)
- security@apache.org (vendor-advisory, Mailing List, Vendor Advisory)
- af854a3a-2127-422b-91ae-364da2661108 (Mailing List, Third Party Advisory)
Frequently asked questions
- What is CVE-2026-40021?
- CVE-2026-40021 is a medium-severity vulnerability in Apache Log4net, classified under Improper Encoding or Escaping of Output. CVSS score: 5.3/10. Published 2026-04-10.
- How severe is CVE-2026-40021?
- Medium severity. CVSS v3 base score is 5.3 out of 10.