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.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
None
No data leak
Integrity
Low
Partial data modification
Availability
None
No disruption
CVSS Vector v3.1
Weakness Type (CWE)
Vulnerable Products 1
| Configuration | From (including) | Up to (excluding) |
|---|---|---|
|
Apache Log4net
cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:*
|
1.2.9
|
3.5.0
|
References 4
https://github.com/apache/logging-log4net/commit/4d2e10f0908199604b4326f9df6d0b…
security@apache.org
https://github.com/apache/logging-log4net/pull/315
security@apache.org
https://lists.apache.org/thread.html/hg8dgh3oy8bp3dhb8nsygk9kw2o401ws
security@apache.org
http://www.openwall.com/lists/oss-security/2026/10/07/15
af854a3a-2127-422b-91ae-364da2661108