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

Medium 5.3 Published 6 Oct 2026 Updated 7 Oct 2026

Attackers can suppress log records for their requests by triggering validation errors in ASP.NET layouts, affecting applications using specific log4net configurations.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-105242?

CVE-2026-105242 is a medium-severity denial of service vulnerability in Apache log4net, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-755

Which versions are affected by CVE-2026-105242?

It affects 1 product.

Products include Apache Log4net.

How do I fix CVE-2026-105242?

No fix has been published for CVE-2026-105242 yet. Limit exposure of the affected software until one is available.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-105242 being exploited?

There is no known exploitation of CVE-2026-105242 in the wild and no public exploit code.

Sources

Also known as DEBIAN-CVE-2026-105242, GHSA-r886-mf8r-26c7, UBUNTU-CVE-2026-105242.