What’s Vulnerable › Vulnerabilities

CVE-2026-105242: Apache log4net: Request validation failure drops the event in the aspnet-request converter

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-06 · updated 2026-10-09
• Weakness: CWE-755

Description

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.

Affected products

• Apache Software Foundation Apache log4net: from 1.2.11 before 3.5.0 — fixed in 3.5.0

How to fix

Upgrade to a fixed version: Apache Software Foundation Apache log4net 3.5.0. Check the vendor advisory for mitigations.

References

• https://github.com/apache/logging-log4net/commit/145203420c579a703008b4b723b6a080757f4964
• https://github.com/apache/logging-log4net/pull/316
• https://lists.apache.org/thread.html/zg6dbqm4ztm7j3c21nfsqj0yxm5yrpdx
• http://www.openwall.com/lists/oss-security/2026/10/07/16

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