Medium · published October 7, 2026
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.
| Product | Versions | Fixed in |
|---|---|---|
| apache/log4net | ≥ 1.2.9, < 3.5.0 | 3.5.0 |