Medium
log4net — security advisory
Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net. A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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-2026-105240
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 02:35 UTC · Revision 1
Source evidence
Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net. A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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-2026-105240
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": "d52f3f8096f347f172f6179629ee6b6037339f5558297cc6b3ac5f20e056f42e",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-105240",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-105240",
"summary": "Improper Neutralization of Null Byte or NUL Character vulnerability in the OutputDebugStringAppender of Apache log4net. A NUL character in logged content ended the debug output record at that point, so everything the layout rendered after it, including exception text and trailing fields, was silently lost. A party whose data reaches a log message could hide the rest of that record. Only applications on Windows that use OutputDebugStringAppender 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-2026-105240",
"products": [
{
"name": {
"value": "log4net",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.2.10+dfsg-6",
"evidence": "/affected/0/versions"
},
{
"value": "1.2.10+dfsg-7",
"evidence": "/affected/0/versions"
},
{
"value": "1.2.10+dfsg-7ubuntu0.16.04.1",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
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"evidence": "/affected/1/package/name"
},
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"affected_versions": [
{
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"evidence": "/affected/1/versions"
},
{
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{
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"affected_versions": [
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"evidence": "/affected/2/versions"
},
{
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"evidence": "/affected/2/versions"
}
]
},
{
"name": {
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"evidence": "/affected/3/package/name"
},
"prerequisites": [],
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"affected_versions": [
{
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"evidence": "/affected/3/versions"
}
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},
{
"name": {
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"evidence": "/affected/4/package/name"
},
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"affected_versions": [
{
"value": "1.2.10+dfsg-8",
"evidence": "/affected/4/versions"
},
{
"value": "1.2.10+dfsg-9",
"evidence": "/affected/4/versions"
}
]
},
{
"name": {
"value": "log4net",
"evidence": "/affected/5/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.2.10+dfsg-9build1",
"evidence": "/affected/5/versions"
},
{
"value": "1.2.10+dfsg-10",
"evidence": "/affected/5/versions"
}
]
},
{
"name": {
"value": "log4net",
"evidence": "/affected/6/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.2.10+dfsg-9",
"evidence": "/affected/6/versions"
},
{
"value": "1.2.10+dfsg-9build1",
"evidence": "/affected/6/versions"
}
]
}
],
"severity": "medium",
"structured": {
"id": "UBUNTU-CVE-2026-105240",
"aliases": [
"UBUNTU-CVE-2026-105240"
],
"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"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "log4net",
"purl": "pkg:deb/ubuntu/log4net?arch=source&distro=xenial",
"ecosystem": "Ubuntu:16.04:LTS"
},
"versions": [
"1.2.10+dfsg-6",
"1.2.10+dfsg-7",
"1.2.10+dfsg-7ubuntu0.16.04.1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-105240.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "liblog4net1.2-cil",
"binary_version": "1.2.10+dfsg-7ubuntu0.16.04.1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
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}
]
}
],
"package": {
"name": "log4net",
"purl": "pkg:deb/ubuntu/log4net?arch=source&distro=bionic",
"ecosystem": "Ubuntu:18.04:LTS"
},
"versions": [
"1.2.10+dfsg-7",
"1.2.10+dfsg-7ubuntu0.18.04.1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-105240.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "liblog4net1.2-cil",
"binary_version": "1.2.10+dfsg-7ubuntu0.18.04.1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
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}
]
}
],
"package": {
"name": "log4net",
"purl": "pkg:deb/ubuntu/log4net?arch=source&distro=focal",
"ecosystem": "Ubuntu:20.04:LTS"
},
"versions": [
"1.2.10+dfsg-7",
"1.2.10+dfsg-7ubuntu0.20.04.1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-105240.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "liblog4net1.2-cil",
"binary_version": "1.2.10+dfsg-7ubuntu0.20.04.1"
}
]
}
},
{
"ranges": [
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],
"package": {
"name": "log4net",
"purl": "pkg:deb/ubuntu/log4net?arch=source&distro=jammy",
"ecosystem": "Ubuntu:22.04:LTS"
},
"versions": [
"1.2.10+dfsg-8"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-105240.json"
},
"ecosystem_specific": {
"binaries": [
{
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},
{
"ranges": [
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"package": {
"name": "log4net",
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"ecosystem": "Ubuntu:24.04:LTS"
},
"versions": [
"1.2.10+dfsg-8",
"1.2.10+dfsg-9"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-105240.json"
},
"ecosystem_specific": {
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}
]
}
},
{
"ranges": [
{
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],
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"ecosystem": "Ubuntu:26.10"
},
"versions": [
"1.2.10+dfsg-9build1",
"1.2.10+dfsg-10"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-105240.json"
},
"ecosystem_specific": {
"binaries": [
{
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"binary_version": "1.2.10+dfsg-10"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
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}
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}
],
"package": {
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"purl": "pkg:deb/ubuntu/log4net?arch=source&distro=resolute",
"ecosystem": "Ubuntu:26.04:LTS"
},
"versions": [
"1.2.10+dfsg-9",
"1.2.10+dfsg-9build1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-105240.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "liblog4net1.2-cil",
"binary_version": "1.2.10+dfsg-9build1"
}
]
}
}
],
"modified": "2026-10-17T12:58:41.586583336Z",
"provider": "osv",
"upstream": [
"CVE-2026-105240"
],
"references": [
"https://ubuntu.com/security/CVE-2026-105240",
"https://www.cve.org/CVERecord?id=CVE-2026-105240",
"https://github.com/apache/logging-log4net/pull/315",
"https://lists.apache.org/thread/gyw2d4ppy82t1vlpdknkfd1nmzp21z17"
]
},
"related_cves": [
{
"value": "CVE-2026-105240",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 358962,
"published_at": "2026-10-06T20:17:00+00:00"
}