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.
Fix
Patch, vendor advisory and mitigation references on NVD 3
- https://github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed Patch
- https://github.com/apache/logging-log4net/pull/315 Patch
- https://lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp Mailing List, Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 5.3 · apacheNVD modified 2026-10-09 15:26
Affected (CPE criteria) 1
cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:*
References 4
- https://github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed Patch
- https://github.com/apache/logging-log4net/pull/315 Patch
- https://lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp Mailing List, Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/10/07/17 Mailing List, Third Party Advisory