Medium 5.3Published Oct 6, 2026

CVE-2026-105243Apache log4net: Oversize EventLogAppender record silently discarded

Updated under an hour ago (2026-10-19 06:30 UTC)

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It affects Apache Software Foundation Apache log4net and 1 other product. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for Apache Software Foundation Apache log4net

Exploited in the last 30 days

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: 5.3 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness (CWE): CWE-778
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: apache
NVD analysis: Analyzed
Record last updated: Oct 7, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Apache Software Foundation Apache log4net apache_software_foundation:apache_log4net (from the name)	from 1.2.9 before 3.5.0	CNA record
apache log4net apache:log4net	from 1.2.9 before 3.5.0	NVD

References

https://github.com/apache/logging-log4net/pull/315patch
https://github.com/apache/logging-log4net/commit/28fbfb25678c48a8cc5bc9b94ead0dddfc39ffedpatch
https://lists.apache.org/thread.html/jr6fj5skv1vnjbc9jmt8bp151p8ow1rpvendor-advisory, mailing-list
http://www.openwall.com/lists/oss-security/2026/10/07/17mailing-list, third-party-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.