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.
Metrics
Affected Vendors & Products
References
History
Fri, 16 Oct 2026 11:30:00 +0000
| Type | Values Removed | Values Added |
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| Metrics |
ssvc
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Tue, 13 Oct 2026 04:15:00 +0000
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| Title | Arbitrary IP Banning via Username Injection in fail2ban SSHD Filter |
Tue, 13 Oct 2026 02:45:00 +0000
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| 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 |
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| References |
| |
| Metrics |
cvssV3_1
|
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
Updated: 2026-10-15T15:04:11.535Z
Status : Awaiting Analysis
Published: 2026-10-13T03:16:40.943
Modified: 2026-10-16T19:55:59.740
Link: CVE-2026-109786
No data.