Vulnerability · Published Oct 6, 2026 · Assigned by apache
CVE-2026-105241Apache log4net: Unencodable content discards a whole SmtpPickupDirAppender batch
Medium 5.3
In plain English
A medium-severity security flaw in Apache log4net from Apache Software Foundation. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.8% (higher than 58% of all known vulnerabilities).
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | log4net | no fix listed | DEBIAN-CVE-2026-105241 |
| Debian:14 | log4net | no fix listed | DEBIAN-CVE-2026-105241 |
| Ubuntu:22.04:LTS | log4net | no fix listed | UBUNTU-CVE-2026-105241 |
| Ubuntu:24.04:LTS | log4net | no fix listed | UBUNTU-CVE-2026-105241 |
| Ubuntu:26.04:LTS | log4net | no fix listed | UBUNTU-CVE-2026-105241 |
| Ubuntu:26.10 | log4net | no fix listed | UBUNTU-CVE-2026-105241 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Apache Software Foundation | Apache log4net | 1.2.9 – before 3.5.0 |
| Apache Software Foundation | Apache log4net | 02e1e115435888485f2e28b414d267e39e799e07 – before 4d2e10f0908199604b4326f9df6d0b43b871e333 |
Weakness: CWE-176 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N