Description
Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net.
A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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 products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Apache Software Foundation | Apache log4net | 1.2.9 – < 3.5.0 | 3.5.0 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | log4net | No fix yet | — |
| Debian 13 | log4net | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | log4net | No fix yet | — |
| Ubuntu 26.04 LTS | log4net | No fix yet | — |
| Ubuntu 24.04 LTS | log4net | No fix yet | — |
| Ubuntu 22.04 LTS | log4net | No fix yet | — |
| Ubuntu 20.04 LTS | log4net | No fix yet | — |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 18.04 LTS | log4net | No fix yet | — |
| Ubuntu 16.04 LTS | log4net | No fix yet | — |
Advisories 1
- WID-SEC-2026-3772 Apache log4net: Mehrere Schwachstellen ermöglichen Manipulation von Dateien BSI CERT-Bund (WID) · Oct 6, 2026