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.
Metrics
CVSS 3.1 5.3/10
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:NWeakness enumeration
Affected software
| Vendor | Product | Versions |
|---|---|---|
| Apache Software Foundation | Apache log4net | >= 1.2.9, < 3.5.0 |
| Apache Software Foundation | Apache log4net | >= 02e1e115435888485f2e28b414d267e39e799e07, < 4d2e10f0908199604b4326f9df6d0b43b871e333 |
References
- https://github.com/apache/logging-log4net/commit/4d2e10f0908199604b4326f9df6d0b43b871e333Patch
- https://github.com/apache/logging-log4net/pull/315Patch
- https://lists.apache.org/thread.html/hg8dgh3oy8bp3dhb8nsygk9kw2o401wsMailing List, Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/10/07/15Mailing List, Third Party Advisory
Timeline
- Published
- Oct 6, 2026
- Last modified
- Oct 9, 2026
- NVD status
- Analyzed