CVE-2026-105243: Apache LOG4NET

Medium severity, CVSS 5.3. EPSS: 0.8% chance of exploitation in the next 30 days.

Insufficient Logging vulnerability in the EventLogAppender of Apache log4net. Long messages were truncated to a fixed size that exceeds what the Windows Event Log accepts once the log and source names are counted, and the event log then stored nothing and reported nothing. A party whose data reaches a log message could suppress the whole record by making it long enough. Only applications on Windows that use EventLogAppender are affected. This issue affects Apache log4net: from 1.2.9 before 3.5.0. Users are recommended to upgrade to version 3.5.0, which fixes the issue.

Affected products

• Apache LOG4NET: from 1.2.9, before 3.5.0 (fixed in 3.5.0)

Published 2026-10-06. Last modified 2026-10-09.