CVE-2026-105241

Apache log4net: Unencodable content discards a whole SmtpPickupDirAppender batch

Published Oct 6, 2026 CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
CPEs cpe:2.3:a:apache:log4net:*:*:*:*:*:*:*:*
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Apache
Apache log4net
Vendors & Products Apache
Apache log4net
Type Values Removed Values Added
Description 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.
Title Apache log4net: Unencodable content discards a whole SmtpPickupDirAppender batch
Weaknesses CWE-176
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
apache
Published
Updated
Oct 7, 2026, 2:45 PM
Reserved
Oct 4, 2026, 4:20 PM
Status
Analyzed
Published
Oct 6, 2026, 8:17 PM
Modified
Oct 9, 2026, 3:29 PM