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CVE-2026-105240

5.3 · MEDIUM

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net.

Published Oct 6, 2026apacheCWE-158EPSS 0.81%

Overview

CVE-2026-105240 is a medium-severity vulnerability affecting apache log4net. It was published on October 6, 2026 and has a CVSS 3.1 base score of 5.3 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net.

A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender are affected.

This issue affects Apache log4net: from 1.2.9 before 3.5.0.

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

Remediation

Check the references section for vendor advisories and patches from apache. Update log4net to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
apachelog4net>= 1.2.9, < 3.5.0Affected

References

GitHubgithub.com/apache/logging-log4net/commit/6046fe9d7f353b49fe995361c071ec2eea8f7ef6GitHubgithub.com/apache/logging-log4net/pull/315Reflists.apache.org/thread.html/gyw2d4ppy82t1vlpdknkfd1nmzp21z17Refwww.openwall.com/lists/oss-security/2026/10/07/18

How CyberStrike helps

Frequently asked questions

What is CVE-2026-105240?

CVE-2026-105240 is a medium-severity vulnerability affecting apache log4net. It was published on October 6, 2026 and has a CVSS 3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-105240?

This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-105240?

Check the references section for vendor advisories and patches from apache. Update log4net to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-105240?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-105240 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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