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.

CVSS 3.1

5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS

0.8% chance of exploitation in the next 30 days; higher than 57% of CVEs (scores of 2026-10-25)

CWE

CWE-116

Published

2026-10-06

Modified

2026-10-09

Record from

the NVD, synced 2026-10-19

Affected

• apache:log4net

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

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