{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-109786", "assignerOrgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca", "state": "PUBLISHED", "assignerShortName": "mitre", "dateReserved": "2026-10-13T02:40:12.792Z", "datePublished": "2026-10-13T02:40:13.899Z", "dateUpdated": "2026-10-13T02:40:13.899Z"}, "containers": {"cna": {"affected": [{"defaultStatus": "unknown", "modules": ["sshd filter"], "platforms": ["Linux", "Unix"], "product": "fail2ban", "programFiles": ["config/filter.d/sshd.conf"], "repo": "https://github.com/fail2ban/fail2ban", "vendor": "fail2ban", "versions": [{"lessThanOrEqual": "1.1.1", "status": "affected", "version": "0.10.5", "versionType": "custom"}]}], "configurations": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "The sshd jail is enabled with the stock filter.d/sshd.conf (any mode: normal, the default, extra, or aggressive). Before 1.1.1 the filter only matches log lines from a process named sshd (OpenSSH before 10, or systems that log as sshd); 1.1.1 also matches OpenSSH 10's sshd-session."}], "value": "The sshd jail is enabled with the stock filter.d/sshd.conf (any mode: normal, the default, extra, or aggressive). Before 1.1.1 the filter only matches log lines from a process named sshd (OpenSSH before 10, or systems that log as sshd); 1.1.1 also matches OpenSSH 10's sshd-session."}], "descriptions": [{"lang": "en", "value": "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": [{"cvssV3_1": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "LOW", "baseScore": 5.3, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L", "version": "3.1"}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"cweId": "CWE-117", "description": "CWE-117 Improper Output Neutralization for Logs", "lang": "en", "type": "CWE"}]}], "providerMetadata": {"orgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca", "shortName": "mitre", "dateUpdated": "2026-10-13T02:40:13.899Z"}, "references": [{"tags": ["patch"], "url": "https://github.com/fail2ban/fail2ban/commit/ddd879d22664904ace24e1255ac6571808c58187"}, {"tags": ["related"], "url": "https://coredump.ws/repos/mail-hardening.git/"}], "solutions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "Apply upstream commit ddd879d22664904ace24e1255ac6571808c58187, or upgrade to the first fail2ban release after 1.1.1 that contains it."}], "value": "Apply upstream commit ddd879d22664904ace24e1255ac6571808c58187, or upgrade to the first fail2ban release after 1.1.1 that contains it."}], "workarounds": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "Override __on_port_opt and __suff in a local filter.d/sshd.local so that only an optional \"port N\" may follow the host address, as in the upstream fix: __on_port_opt = (?: port \\d+)? and __suff = %(__on_port_opt)s(?: \\[preauth\\])?\\s*. Add the administrator's own addresses to ignoreip."}], "value": "Override __on_port_opt and __suff in a local filter.d/sshd.local so that only an optional \"port N\" may follow the host address, as in the upstream fix: __on_port_opt = (?: port \\d+)? and __suff = %(__on_port_opt)s(?: \\[preauth\\])?\\s*. Add the administrator's own addresses to ignoreip."}], "x_generator": {"engine": "CVE-Request-form 0.0.1"}, "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:fail2ban:fail2ban:*:*:*:*:*:*:*:*", "versionStartIncluding": "0.10.5", "versionEndIncluding": "1.1.1"}]}]}]}}}

{}

{"affected": [{"affectedData": [{"defaultStatus": "unknown", "modules": ["sshd filter"], "platforms": ["Linux", "Unix"], "product": "fail2ban", "programFiles": ["config/filter.d/sshd.conf"], "repo": "https://github.com/fail2ban/fail2ban", "vendor": "fail2ban", "versions": [{"lessThanOrEqual": "1.1.1", "status": "affected", "version": "0.10.5", "versionType": "custom"}]}], "source": "cve@mitre.org"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "id": "CVE-2026-109786", "lastModified": "2026-10-13T03:16:40.943", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "LOW", "baseScore": 5.3, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 1.4, "source": "cve@mitre.org", "type": "Secondary"}]}, "published": "2026-10-13T03:16:40.943", "references": [{"source": "cve@mitre.org", "url": "https://coredump.ws/repos/mail-hardening.git/"}, {"source": "cve@mitre.org", "url": "https://github.com/fail2ban/fail2ban/commit/ddd879d22664904ace24e1255ac6571808c58187"}], "sourceIdentifier": "cve@mitre.org", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-117"}], "source": "cve@mitre.org", "type": "Primary"}]}

{}

{"affected": [{"configurations": [{"platform": ["linux", "unix"], "status": "affected", "versions": {"scheme": "semver", "value": "[0.10.5,1.1.1]"}}], "enrichment": {"confidence": 95.0, "confidence_source": "inferred", "scores": [{"score": 95.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "fail2ban", "source": "cna", "vendor": "fail2ban"}, "product": "fail2ban", "vendor": "fail2ban"}], "created": "2026-10-13T04:00:16.312500+00:00", "title": "Arbitrary IP Banning via Username Injection in fail2ban SSHD Filter", "updated": "2026-10-13T04:15:15.085915+00:00", "vendors": ["fail2ban", "fail2ban$PRODUCT$fail2ban"]}