# CVE-2026-105244: Apache log4net improper character escaping in RemoteSyslogAppender

Source: https://junglewise.ai/threats/cve-2026-105244-improper-encoding-or-escaping-of-output-vulnerability-in-the  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-06. Updated: 2026-10-06  
License: CC BY 4.0 with a link back

CVE-2026-105244 · Severity: medium · CVSS 5.3 · Published 2026-10-06

Apache log4net is a .NET logging library widely used to record application events and diagnostic information. The RemoteSyslogAppender component silently removes non-ASCII characters and control characters like tabs from log messages instead of escaping them, allowing an attacker to craft log entries where distinct values appear identical—for example, a username with an invisible zero-width space appearing identical to "admin"—potentially causing log-based access control bypass or data confusion.

Technologies: [Apache Log4net](https://junglewise.ai/threats/technologies/log4net). Vendors: [Apache](https://junglewise.ai/threats/vendors/apache).

## Quick answers

**Is CVE-2026-105244 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-105244 being exploited in the wild.

**How severe is CVE-2026-105244?** Medium severity, with a CVSS score of 5.3, published 6 October 2026.

**Which products and versions are affected?** Apache Log4net 1.2.12 before 3.5.0.

**Is there a fix for CVE-2026-105244?** Yes: fixed in 3.5.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-105244 attacked?** It is attacked over the network or with local access, in a software library.

**Am I affected by CVE-2026-105244?** Check whether you run Apache Log4net at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 3.5.0

## Technical details

The RemoteSyslogAppender fails to properly escape characters outside the visible ASCII and space range as required by RFC 3164, instead silently deleting them. This occurs in the message encoding path before remote syslog transmission. An attacker controlling data that reaches a log message (application user input, HTTP headers, etc.) can inject invisible Unicode characters or control characters to create log collisions or obfuscate audit trails.

## Affected products

- Apache log4net 1.2.12 before 3.5.0

## Timeline

- 2026-10-06: disclosed

## References

- [https://nuget.org/packages](https://nuget.org/packages)
- [https://github.com/apache/logging-log4net/commit/77717061b20d4346b6c0ce6b54643d85fb348bc7](https://github.com/apache/logging-log4net/commit/77717061b20d4346b6c0ce6b54643d85fb348bc7)

## Related threats

- [Apache log4net insufficient logging in EventLogAppender](https://junglewise.ai/threats/cve-2026-105243-insufficient-logging-vulnerability-in-the-eventlogappender-of)
- [Apache log4net improper handling of exceptions in aspnet-request pattern converter](https://junglewise.ai/threats/cve-2026-105242-improper-handling-of-exceptional-conditions-vulnerability-in-the)
- [Apache log4net improper Unicode encoding in SmtpPickupDirAppender](https://junglewise.ai/threats/cve-2026-105241-improper-handling-of-unicode-encoding-vulnerability-in-the)
- [Apache log4net null byte handling in OutputDebugStringAppender](https://junglewise.ai/threats/cve-2026-105240-improper-neutralization-of-null-byte-or-nul-character)
- [Apache log4net null byte injection in EventLogAppender](https://junglewise.ai/threats/cve-2026-105239-improper-neutralization-of-null-byte-or-nul-character)