---
id: CVE-2026-109786
title: >-
  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
summary: >-
  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…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'
cwe:
  - CWE-117
published: '2026-10-13'
updated: '2026-10-13'
sourceUpdated: '2026-10-13T03:16:40.943'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-109786'
references:
  - url: 'https://coredump.ws/repos/mail-hardening.git/'
    label: cve@mitre.org
  - url: >-
      https://github.com/fail2ban/fail2ban/commit/ddd879d22664904ace24e1255ac6571808c58187
    label: cve@mitre.org
tags:
  - nvd
ingestedAt: '2026-10-13T04:14:33.875Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.