Is CVE-2026-105241 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-105241 being exploited in the wild.

How severe is CVE-2026-105241?

Medium severity, with a CVSS score of 5.3, published 6 October 2026.

Which products and versions are affected?

Apache Log4net 1.2.9 before 3.5.0.

Is there a fix for CVE-2026-105241?

Yes: fixed in 3.5.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-105241 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-105241?

Check whether you run Apache Log4net at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-105241: Apache log4net improper Unicode encoding in SmtpPickupDirAppender

CVE-2026-105241 · Severity: medium · CVSS 5.3 · Published 2026-10-06

Apache log4net is a widely used logging framework for .NET applications. A flaw in its email appender component causes it to discard log messages when encountering certain malformed Unicode characters, leaving truncated emails in the pickup directory. An attacker who can inject data into logged messages could suppress records of their own or other events, potentially hiding security-relevant audit trails.

Technologies: Apache Log4net. Vendors: Apache.

Quick answers

Is CVE-2026-105241 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-105241 being exploited in the wild.
How severe is CVE-2026-105241?: Medium severity, with a CVSS score of 5.3, published 6 October 2026.
Which products and versions are affected?: Apache Log4net 1.2.9 before 3.5.0.
Is there a fix for CVE-2026-105241?: Yes: fixed in 3.5.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-105241 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-105241?: Check whether you run Apache Log4net at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

Fixed in: 3.5.0

Technical details

The SmtpPickupDirAppender fails to handle unpaired UTF-16 surrogates during encoding, causing File.CreateText to throw an exception. Rather than handling the problematic event alone, the entire buffered batch of events is discarded and a truncated mail file is left in the pickup directory. An attacker who can influence logged data can trigger this condition to suppress audit records; only applications using SmtpPickupDirAppender are affected.

Affected products

Apache log4net 1.2.9 before 3.5.0

Timeline

2026-10-06: disclosed

References

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