Bug 2547134 (CVE-2026-105242)

Summary: CVE-2026-105242 log4net: log4net: Audit log suppression via crafted request parameters
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in log4net. A remote attacker can exploit this issue by sending a crafted request containing content such as markup that triggers ASP.NET request validation. When log4net attempts to parse the request parameters, an unhandled exception occurs, causing the logging system to discard the entire log event. Consequently, an attacker can suppress log records of their own requests and evade security monitoring.
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Bug Depends On: 2547385, 2547386    
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Description OSIDB Bzimport 2026-10-06 20:02:28 UTC 
Improper Handling of Exceptional Conditions vulnerability in the aspnet-request pattern converter of Apache log4net.

Reading request parameters triggers ASP.NET request validation, so a request carrying content such as markup made the layout throw and the appender discarded the whole event. A sender could suppress the log record of their own request. Only applications on ASP.NET for .NET Framework whose layout uses %aspnet-request are affected.

This issue affects Apache log4net: from 1.2.11 before 3.5.0.

Users are recommended to upgrade to version 3.5.0, which fixes the issue.