Medium
log4net — security advisory
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.
- Products
- log4net
- Affected versions
- 1.2.10+dfsg-10, 1.2.10+dfsg-6, 1.2.10+dfsg-7, 1.2.10+dfsg-7ubuntu0.16.04.1, 1.2.10+dfsg-7ubuntu0.18.04.1, 1.2.10+dfsg-7ubuntu0.20.04.1, 1.2.10+dfsg-8, 1.2.10+dfsg-9, 1.2.10+dfsg-9build1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-105241
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 01:58 UTC · Revision 1
Source evidence
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.
osv:UBUNTU-CVE-2026-105241
log4net
Fixed versions: Not specified
log4net
Fixed versions: Not specified
log4net
Fixed versions: Not specified
log4net
Fixed versions: Not specified
log4net
Fixed versions: Not specified
log4net
Fixed versions: Not specified
log4net
Fixed versions: Not specified
Complete source record
{
"id": "2514868108397d86da9c4d61dfb05e69a2f9d1409d384cdbd1245888bd41319a",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-105241",
"method": "structured",
"payload": {
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"title": "UBUNTU-CVE-2026-105241",
"summary": "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.",
"evidence": "osv:UBUNTU-CVE-2026-105241",
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"severity": "medium",
"structured": {
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"aliases": [
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"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"
},
{
"type": "Ubuntu",
"score": "medium"
}
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"modified": "2026-10-17T12:57:59.492831918Z",
"provider": "osv",
"upstream": [
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],
"references": [
"https://ubuntu.com/security/CVE-2026-105241",
"https://www.cve.org/CVERecord?id=CVE-2026-105241",
"https://github.com/apache/logging-log4net/pull/315",
"https://lists.apache.org/thread/hg8dgh3oy8bp3dhb8nsygk9kw2o401ws"
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},
"source_id": "core-osv",
"document_id": 357826,
"published_at": "2026-10-06T20:17:00+00:00"
}