Severity: moderate
CVSS 3.1: 5.3 (medium) CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Affected versions:
- Apache log4net 1.2.9 before 3.5.0
- Apache log4net 02e1e115435888485f2e28b414d267e39e799e07 before
4d2e10f0908199604b4326f9df6d0b43b871e333
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.
Credit:
The Apache Software Foundation (finder)
Claude Security (tool)
Jan Friedrich (remediation developer)
References:
https://github.com/apache/logging-log4net/pull/315
https://github.com/apache/logging-log4net/commit/4d2e10f0908199604b4326f9df6d0b43b871e333
https://logging.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-105241
