Vulnerability · Published Oct 6, 2026 · Assigned by apache
CVE-2026-105239Apache log4net: NUL character truncates EventLogAppender records
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 Neutralization of Null Byte or NUL Character vulnerability in the EventLogAppender of Apache log4net. A NUL character in logged content ended the Windows Event Log record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently not stored. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use EventLogAppender 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-2026-105239 |
| Debian:14 | log4net | no fix listed | DEBIAN-CVE-2026-105239 |
| Ubuntu:22.04:LTS | log4net | no fix listed | UBUNTU-CVE-2026-105239 |
| Ubuntu:24.04:LTS | log4net | no fix listed | UBUNTU-CVE-2026-105239 |
| Ubuntu:26.04:LTS | log4net | no fix listed | UBUNTU-CVE-2026-105239 |
| Ubuntu:26.10 | log4net | no fix listed | UBUNTU-CVE-2026-105239 |
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 dc5855a0720c91590fd7a81d729ea01fdd69e000 |
Weakness: CWE-158 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N