CVE-2026-105243: CWE-778 Insufficient Logging in Apache Software Foundation Apache log4net
Description
CVE-2026-105243 is an insufficient logging vulnerability in Apache log4net's EventLogAppender on Windows. Long log messages exceeding Windows Event Log size limits are truncated, causing the event log to store nothing and report no error. This allows an attacker to suppress entire log records by crafting overly long messages. The issue affects Apache log4net versions from 1.2.9 up to but not including 3.5.0. Upgrading to version 3.5.0 resolves the problem.
CVSS v3.1
Score 5.3medium
Affected software
Apache Software Foundation
Apache log4net
Apache Software Foundation
Apache log4net
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Apache log4net's EventLogAppender on Windows truncates long messages to a fixed size that, when combined with log and source names, exceeds Windows Event Log limits. This results in the event log discarding the entire log entry silently without storing or reporting it. Consequently, an attacker able to influence log message content can suppress logging of events by making messages sufficiently long. This vulnerability affects Apache log4net versions >=1.2.9 and <3.5.0. The issue is fixed in version 3.5.0.
Potential Impact
The vulnerability allows suppression of log records in Windows Event Logs by causing the EventLogAppender to discard entries with overly long messages silently. This can hinder forensic analysis and incident detection by preventing certain events from being logged. There is no direct confidentiality or availability impact, but integrity of logging is compromised.
Mitigation Recommendations
Users should upgrade Apache log4net to version 3.5.0 or later, where this issue is fixed. No other mitigations are indicated. Patch status is confirmed by vendor advisory information.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- apache
- Date Reserved
- 2026-10-04T16:21:38.272Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6ac5544a2cdf04f656d9e12c
Added to database: 10/06/2026, 20:04:26 UTC
Last enriched: 10/06/2026, 20:19:06 UTC
Last updated: 10/06/2026, 20:19:15 UTC
Views: 4
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