Vulnerability · Published Oct 6, 2026 · Assigned by apache
CVE-2026-105244Apache log4net: RemoteSyslogAppender silently deletes non-ASCII content
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 Encoding or Escaping of Output vulnerability in the RemoteSyslogAppender of Apache log4net. Every character outside visible ASCII and space was removed from the record instead of being escaped, so non-ASCII text and control characters such as tabs disappeared without notice. A party whose data reaches a log message could make a distinct value look identical in the record, for example a user name holding a zero-width space logged as admin. Only applications that use RemoteSyslogAppender are affected. This issue affects Apache log4net: from 1.2.12 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-2026-105244 |
| Debian:14 | log4net | no fix listed | DEBIAN-CVE-2026-105244 |
| Ubuntu:22.04:LTS | log4net | no fix listed | UBUNTU-CVE-2026-105244 |
| Ubuntu:24.04:LTS | log4net | no fix listed | UBUNTU-CVE-2026-105244 |
| Ubuntu:26.04:LTS | log4net | no fix listed | UBUNTU-CVE-2026-105244 |
| Ubuntu:26.10 | log4net | no fix listed | UBUNTU-CVE-2026-105244 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Apache Software Foundation | Apache log4net | 1.2.12 – before 3.5.0 |
| Apache Software Foundation | Apache log4net | 56a2e146e21ff4737e1ff3ec308810e667873947 – before 77717061b20d4346b6c0ce6b54643d85fb348bc7 |
Weakness: CWE-116 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N