Vulnerability Details 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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.008
EPSS Ranking 55.6%
CVSS Severity
CVSS v3 Score 5.3
References
Products affected by CVE-2026-105243
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cpe:2.3:a:apache:log4net:1.2.10
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cpe:2.3:a:apache:log4net:1.2.11
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cpe:2.3:a:apache:log4net:1.2.12
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cpe:2.3:a:apache:log4net:1.2.13
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cpe:2.3:a:apache:log4net:1.2.15
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cpe:2.3:a:apache:log4net:1.2.9
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cpe:2.3:a:apache:log4net:1.2.9_beta
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cpe:2.3:a:apache:log4net:2.0.10
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cpe:2.3:a:apache:log4net:2.0.11
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cpe:2.3:a:apache:log4net:2.0.12
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cpe:2.3:a:apache:log4net:2.0.13
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cpe:2.3:a:apache:log4net:2.0.14
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cpe:2.3:a:apache:log4net:2.0.15
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cpe:2.3:a:apache:log4net:2.0.16
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cpe:2.3:a:apache:log4net:2.0.17
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cpe:2.3:a:apache:log4net:2.0.6
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cpe:2.3:a:apache:log4net:2.0.7
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cpe:2.3:a:apache:log4net:2.0.8
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cpe:2.3:a:apache:log4net:2.0.9
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cpe:2.3:a:apache:log4net:3.0.0
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cpe:2.3:a:apache:log4net:3.0.1
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cpe:2.3:a:apache:log4net:3.0.2
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cpe:2.3:a:apache:log4net:3.0.3
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cpe:2.3:a:apache:log4net:3.0.4
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cpe:2.3:a:apache:log4net:3.0.5
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cpe:2.3:a:apache:log4net:3.1.0
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cpe:2.3:a:apache:log4net:3.2.0
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cpe:2.3:a:apache:log4net:3.3.0
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cpe:2.3:a:apache:log4net:3.3.1
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cpe:2.3:a:apache:log4net:3.3.2
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cpe:2.3:a:apache:log4net:3.4.0
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cpe:2.3:a:apache:log4net:3.4.1