CVE-2026-40021
Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescaped XML 1.0 forbidden characters
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 3.3.0, fail to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets in MDC property keys and values, as well as the identity field that may carry attacker-influenced data. This causes an exception during serialization and the silent loss of the affected log event. An attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity. Users are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue.
| CWE | CWE-116 |
| Vendor | apache software foundation |
| Product | apache log4net |
| Published | Apr 10, 2026 |
| Last Updated | Apr 10, 2026 |
Get instant alerts for apache software foundation apache log4net
Be the first to know when new unknown vulnerabilities affecting apache software foundation apache log4net are published — delivered to Slack, Telegram or Discord.