What is CVE-2026-105239?

CVE-2026-105239 is a medium-severity vulnerability in Apache Software Foundation Log4net, classified under CWE-158. CVSS score: 5.3/10. Published 2026-10-06.

How severe is CVE-2026-105239?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Apache Software Foundation Log4net

CVE-2026-105239

Improper Neutralization of Null Byte or NUL Character vulnerability in the EventLogAppender of Apache log4net. A NUL character in logged content ended the Windows Event Log record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently not stored. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use EventLogAppender 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.

Published 2026-10-06 · last modified 2026-10-07.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Apache Software Foundation Log4net

Weakness classification (CWE)

CWE-158

References

Frequently asked questions

What is CVE-2026-105239?: CVE-2026-105239 is a medium-severity vulnerability in Apache Software Foundation Log4net, classified under CWE-158. CVSS score: 5.3/10. Published 2026-10-06.
How severe is CVE-2026-105239?: Medium severity. CVSS v3 base score is 5.3 out of 10.