Bug 2547129 (CVE-2026-105244)

Summary:	CVE-2026-105244 log4net: log4net: Log manipulation via improper character escaping in RemoteSyslogAppender
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in the RemoteSyslogAppender component of log4net. Non-standard and invisible characters in log messages are stripped rather than safely escaped. An attacker who can supply data that is written to logs can exploit this behavior to falsify or obfuscate log entries, potentially making malicious records appear identical to legitimate identifiers. This issue compromises log integrity and can mislead security monitoring and audit investigations.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2547387, 2547388
Bug Blocks:

Description OSIDB Bzimport 2026-10-06 20:02:09 UTC

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.