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.

CVSS 3.1

5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS

0.8% chance of exploitation in the next 30 days; higher than 56% of CVEs (scores of 2026-10-25)

CWE

CWE-778

Published

2026-10-06

Modified

2026-10-09

Record from

the NVD, synced 2026-10-19

Affected

• apache:log4net

References

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

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