{"id":"UBUNTU-CVE-2026-109786","details":"In fail2ban 0.10.5 through 1.1.1 before ddd879d, the sshd filter (config/filter.d/sshd.conf) accepts an \"on \u003ctoken\u003e\" 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.","modified":"2026-10-17T12:58:03.252702294Z","published":"2026-10-15T00:00:00Z","upstream":["CVE-2026-109786"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-109786"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-109786"},{"type":"REPORT","url":"https://coredump.ws/repos/mail-hardening.git/"},{"type":"REPORT","url":"https://github.com/fail2ban/fail2ban/commit/ddd879d22664904ace24e1255ac6571808c58187"}],"affected":[{"package":{"name":"fail2ban","ecosystem":"Ubuntu:Pro:14.04:LTS","purl":"pkg:deb/ubuntu/fail2ban?arch=source&distro=esm-infra-legacy%2Ftrusty"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.8.10-3","0.8.11~pre1+git29-gccd2657-1","0.8.11-1","0.8.11-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"0.8.11-1ubuntu0.1~esm1","binary_name":"fail2ban"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-109786.json"}},{"package":{"name":"fail2ban","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/fail2ban?arch=source&distro=esm-apps%2Fxenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.9.3-1","0.9.3-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"fail2ban","binary_version":"0.9.3-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-109786.json"}},{"package":{"name":"fail2ban","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/fail2ban?arch=source&distro=esm-apps%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.9.7-2","0.10.2-1","0.10.2-2","0.10.2-2ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"0.10.2-2ubuntu0.1~esm1","binary_name":"fail2ban"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-109786.json"}},{"package":{"name":"fail2ban","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/fail2ban?arch=source&distro=esm-apps%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.10.2-2.1","0.11.1-1","0.11.1-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"fail2ban","binary_version":"0.11.1-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-109786.json"}},{"package":{"name":"fail2ban","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/fail2ban?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.11.2-2","0.11.2-4","0.11.2-5","0.11.2-6"],"ecosystem_specific":{"binaries":[{"binary_name":"fail2ban","binary_version":"0.11.2-6"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-109786.json"}},{"package":{"name":"fail2ban","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/fail2ban?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.0.2-2","1.0.2-3","1.0.2-3ubuntu0.1"],"ecosystem_specific":{"binaries":[{"binary_name":"fail2ban","binary_version":"1.0.2-3ubuntu0.1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-109786.json"}},{"package":{"name":"fail2ban","ecosystem":"Ubuntu:26.10","purl":"pkg:deb/ubuntu/fail2ban?arch=source&distro=stonking"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.1.0-9","1.1.0-10","1.1.0-11"],"ecosystem_specific":{"binaries":[{"binary_version":"1.1.0-11","binary_name":"fail2ban"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-109786.json"}},{"package":{"name":"fail2ban","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/fail2ban?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.1.0-8","1.1.0-9"],"ecosystem_specific":{"binaries":[{"binary_name":"fail2ban","binary_version":"1.1.0-9"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-109786.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},{"type":"Ubuntu","score":"medium"}]}