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CVE-2026-105241

5.3 · MEDIUM

Improper Handling of Unicode Encoding vulnerability in the SmtpPickupDirAppender of Apache log4net.

Published Oct 6, 2026apacheCWE-176EPSS 0.82%

Overview

CVE-2026-105241 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 Handling of Unicode Encoding vulnerability in the SmtpPickupDirAppender of Apache log4net.

Content that the mail file writer cannot encode, such as an unpaired UTF-16 surrogate, made the write throw. Every buffered event in the batch was discarded, not only the one carrying the content, and a truncated mail could be left in the pickup directory. A party whose data reaches a log message could suppress the records of other events. Only applications that use SmtpPickupDirAppender 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/4d2e10f0908199604b4326f9df6d0b43b871e333GitHubgithub.com/apache/logging-log4net/pull/315Reflists.apache.org/thread.html/hg8dgh3oy8bp3dhb8nsygk9kw2o401wsRefwww.openwall.com/lists/oss-security/2026/10/07/15

How CyberStrike helps

Frequently asked questions

What is CVE-2026-105241?

CVE-2026-105241 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-2026-105241?

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-2026-105241?

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-2026-105241?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-105241 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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