CVE-2026-105241
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.
How to fix
- apache log4net3.5.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| apache log4net | 1.2.9 ≤ v < 3.5.0 | 3.5.0 |
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