Disclosure summary
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.
Source-reported weakness categories
CWE-176
Source-specific records & product guidance
Sources retain their own attribution and scoring. Follow the original record to confirm affected versions, fixed releases, and configuration conditions.
NIST National Vulnerability Database · NVD-CVE-2026-105241
Open original source · Updated Oct 09, 2026
Only CPE matches marked vulnerable=true are indexed. AND/OR platform conditions must be checked in the original NVD record.
| Vendor | Product / association | Version / bounds |
|---|---|---|
| apache | log4net | * {"versionStartIncluding":"1.2.9","versionEndExcluding":"3.5.0"} |
Original records & references
- NIST NVD record
- CVE Program record
- github.com — Patch
- github.com — Patch
- lists.apache.org — Mailing List, Vendor Advisory
PUBLISHED 2026-10-06T16:17:15-04:00
MODIFIED 2026-10-09T11:29:42-04:00
INGESTED 2026-10-10T20:50:46-04:00