Medium
fail2ban — security advisory
In fail2ban 0.10.5 through 1.1.1 before ddd879d, the sshd filter (config/filter.d/sshd.conf) accepts an "on " suffix after the host address. Because OpenSSH logs the offered username verbatim, a remote unauthenticated attacker can use a username such as "x VICTIM-SOURCE-IP-ADDRESS on" to make fail2ban associate failed login attempts with an arbitrary source IP address and ban it (e.g., to block logins from a legitimate user). The default filter mode is affected.
- Products
- fail2ban
- Affected versions
- 1.0.2-2, 1.0.2-3, 1.1.0-1, 1.1.0-10, 1.1.0-11, 1.1.0-2, 1.1.0-3, 1.1.0-4, 1.1.0-6, 1.1.0-7, 1.1.0-8, 1.1.0-9, 1.1.1-1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-109786
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 23:07 UTC · Revision 1
Source evidence
In fail2ban 0.10.5 through 1.1.1 before ddd879d, the sshd filter (config/filter.d/sshd.conf) accepts an "on " suffix after the host address. Because OpenSSH logs the offered username verbatim, a remote unauthenticated attacker can use a username such as "x VICTIM-SOURCE-IP-ADDRESS on" to make fail2ban associate failed login attempts with an arbitrary source IP address and ban it (e.g., to block logins from a legitimate user). The default filter mode is affected.
osv:DEBIAN-CVE-2026-109786
fail2ban
Fixed versions: Not specified
fail2ban
Fixed versions: Not specified
fail2ban
Fixed versions: Not specified
Complete source record
{
"id": "74771aa6510d4ec8e96b488a9d5ecdd0586f06fd9e769edea9d4b5fd4dda7dd6",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2026-109786",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2026-109786",
"summary": "In fail2ban 0.10.5 through 1.1.1 before ddd879d, the sshd filter (config/filter.d/sshd.conf) accepts an \"on \" suffix after the host address. Because OpenSSH logs the offered username verbatim, a remote unauthenticated attacker can use a username such as \"x VICTIM-SOURCE-IP-ADDRESS on\" to make fail2ban associate failed login attempts with an arbitrary source IP address and ban it (e.g., to block logins from a legitimate user). The default filter mode is affected.",
"evidence": "osv:DEBIAN-CVE-2026-109786",
"products": [
{
"name": {
"value": "fail2ban",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.0.2-2",
"evidence": "/affected/0/versions"
},
{
"value": "1.0.2-3",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-1",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-10",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-11",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-2",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-3",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-4",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-6",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-7",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-8",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.0-9",
"evidence": "/affected/0/versions"
},
{
"value": "1.1.1-1",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "fail2ban",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.1.0-10",
"evidence": "/affected/1/versions"
},
{
"value": "1.1.0-11",
"evidence": "/affected/1/versions"
},
{
"value": "1.1.0-8",
"evidence": "/affected/1/versions"
},
{
"value": "1.1.0-9",
"evidence": "/affected/1/versions"
},
{
"value": "1.1.1-1",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "fail2ban",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1.1.0-10",
"evidence": "/affected/2/versions"
},
{
"value": "1.1.0-11",
"evidence": "/affected/2/versions"
},
{
"value": "1.1.0-8",
"evidence": "/affected/2/versions"
},
{
"value": "1.1.0-9",
"evidence": "/affected/2/versions"
},
{
"value": "1.1.1-1",
"evidence": "/affected/2/versions"
}
]
}
],
"severity": "medium",
"structured": {
"id": "DEBIAN-CVE-2026-109786",
"aliases": [
"DEBIAN-CVE-2026-109786"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "fail2ban",
"purl": "pkg:deb/debian/fail2ban?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"versions": [
"1.0.2-2",
"1.0.2-3",
"1.1.0-1",
"1.1.0-10",
"1.1.0-11",
"1.1.0-2",
"1.1.0-3",
"1.1.0-4",
"1.1.0-6",
"1.1.0-7",
"1.1.0-8",
"1.1.0-9",
"1.1.1-1"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-109786.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "fail2ban",
"purl": "pkg:deb/debian/fail2ban?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"versions": [
"1.1.0-10",
"1.1.0-11",
"1.1.0-8",
"1.1.0-9",
"1.1.1-1"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-109786.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "fail2ban",
"purl": "pkg:deb/debian/fail2ban?arch=source&distro=forky",
"ecosystem": "Debian:14"
},
"versions": [
"1.1.0-10",
"1.1.0-11",
"1.1.0-8",
"1.1.0-9",
"1.1.1-1"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-109786.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-23T17:47:35.049161922Z",
"provider": "osv",
"upstream": [
"CVE-2026-109786"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2026-109786"
]
},
"related_cves": [
{
"value": "CVE-2026-109786",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 417758,
"published_at": "2026-10-13T03:16:40.943+00:00"
}