In fail2ban 0.10.5 through 1.1.1 before ddd879d, the sshd filter (config/filter.d/sshd.conf) accepts an "on <token>" 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.
History

Fri, 16 Oct 2026 11:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

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


Tue, 13 Oct 2026 04:15:00 +0000

Type Values Removed Values Added
Title Arbitrary IP Banning via Username Injection in fail2ban SSHD Filter

Tue, 13 Oct 2026 02:45:00 +0000

Type Values Removed Values Added
Description In fail2ban 0.10.5 through 1.1.1 before ddd879d, the sshd filter (config/filter.d/sshd.conf) accepts an "on <token>" 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.
First Time appeared Fail2ban
Fail2ban fail2ban
Weaknesses CWE-117
CPEs cpe:2.3:a:fail2ban:fail2ban:*:*:*:*:*:*:*:*
Vendors & Products Fail2ban
Fail2ban fail2ban
References
Metrics cvssV3_1

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


cve-icon MITRE

Status: PUBLISHED

Assigner: mitre

Published: 2026-10-13T02:40:13.899Z

Updated: 2026-10-15T15:04:19.106Z

Reserved: 2026-10-13T02:40:12.792Z

Link: CVE-2026-109786

cve-icon Vulnrichment

Updated: 2026-10-15T15:04:11.535Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-13T03:16:40.943

Modified: 2026-10-16T19:55:59.740

Link: CVE-2026-109786

cve-icon Redhat

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