Improper Neutralization of Null Byte or NUL Character vulnerability in the EventLogAppender of Apache log4net. A NUL character in logged content ended the Windows Event Log record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently not stored. A party whose data reaches a log message could hide the rest of that record. 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/dc5855a0720c91590fd7a81d729ea01fdd69e000 Patch
- https://github.com/apache/logging-log4net/pull/315 Patch
- https://lists.apache.org/thread.html/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq 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 15:44
Affected (CPE criteria) 1
cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:*
References 4
- https://github.com/apache/logging-log4net/commit/dc5855a0720c91590fd7a81d729ea01fdd69e000 Patch
- https://github.com/apache/logging-log4net/pull/315 Patch
- https://lists.apache.org/thread.html/9fx1qo5hc0tg8ym0t6p9gt1zpb2qlxpq Mailing List, Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/10/07/14 Mailing List, Third Party Advisory