CVE-2026-105244: Improper Encoding (CVSS 5.3)

Description

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net. Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected. This issue affects Apache log4net: from 1.2.12 before 3.5.0. Users are recommended to upgrade to version 3.5.0, which fixes the issue.

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CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS — Exploit Prediction

0.0034

Probability of exploitation

0.25%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-116 CWE-116

References

Other References

https://github.com/apache/logging-log4net/commit/77717061b20d4346b6c0ce6b54643d85fb348bc7 https://github.com/apache/logging-log4net/pull/315 https://lists.apache.org/thread.html/q7649hhdodthoqw8jsjgtnb4m8qfy6d6 http://www.openwall.com/lists/oss-security/2026/10/07/19

Frequently Asked Questions

What is CVE-2026-105244? +

Improper Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net. Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected. This issue affects Apache log4net: from 1.2.12 before 3.5.0. Users are recommended to upgrade to version 3.5.0, which fixes the issue. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-105244? +

CVE-2026-105244 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0034, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-105244? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-105244