CVE-2026-105243

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.

Score

CVSS 3.1 5.3 Medium

Status

Analyzed - security@apache.org

Published

2026-10-06

Last modified

2026-10-09

Weaknesses

CWE-778

Affected products

• Log4net (Apache)
• Apache Log4net (Apache Software Foundation)

References

• https://github.com/apache/logging-log4net/pull/315
• https://github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffed
• https://lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rp
• http://www.openwall.com/lists/oss-security/2026/10/07/17