Improper Output Neutralization for Logs Affecting log4net package, versions [,3.5.0)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published7 Oct 2026
- disclosed6 Oct 2026
- creditUnknown
Introduced: 6 Oct 2026
NewCVE-2026-105242 (opens in a new tab)How to fix?
Upgrade log4net to version 3.5.0 or higher.
Overview
Affected versions of this package are vulnerable to Improper Output Neutralization for Logs in the %aspnet-request pattern converter, which reads HttpRequest.Params and so triggers ASP.NET request validation on the query string, form, and cookies at first access, raising an HttpRequestValidationException inside the layout. An attacker can suppress the log record of their own request entirely, since the appender discards the event when the layout throws, by sending a request carrying content that request validation rejects, such as <script>. This affects only ASP.NET applications on .NET Framework whose layout uses %aspnet-request.