Bug 2547130 (CVE-2026-105241)

Summary: CVE-2026-105241 log4net: log4net: Log event suppression via improper Unicode handling in SmtpPickupDirAppender
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Apache log4net. An attacker who can supply data that is recorded in system logs can submit unencodable Unicode characters, triggering an encoding error in the SmtpPickupDirAppender component. When this failure occurs, the application discards all buffered log messages in the current batch rather than only the malformed entry. This issue allows an attacker to suppress other event records and compromise the completeness of audit logs.
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Bug Depends On: 2547383, 2547384    
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Description OSIDB Bzimport 2026-10-06 20:02:13 UTC 
Improper Handling of Unicode Encoding vulnerability in the SmtpPickupDirAppender of Apache log4net.

Content that the mail file writer cannot encode, such as an unpaired UTF-16 surrogate, made the write throw. Every buffered event in the batch was discarded, not only the one carrying the content, and a truncated mail could be left in the pickup directory. A party whose data reaches a log message could suppress the records of other events. Only applications that use SmtpPickupDirAppender 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.