CVE-2021-40456
Status: ModifiedHigh (7.5)—
Windows AD FS Security Feature Bypass Vulnerability
CVSS
- Version: 3.1
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- Base score: 7.5
Exploitation probability (EPSS)
- Probability of exploitation in the next 30 days: 2.34%
- Percentile among all scored CVEs: 83
- Score date: 10/16/2026
EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).
Affected technologies (3)
CWEs
- NVD-CWE-noinfo
- CWE-863
References
Raw JSON (NVD)
Show
{
"id": "CVE-2021-40456",
"cveTags": [],
"metrics": {
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2021-40456",
"role": "CISA Coordinator",
"options": [
{
"exploitation": "none"
},
{
"automatable": "yes"
},
{
"technicalImpact": "partial"
}
],
"version": "2.0.3",
"timestamp": "2024-07-18T20:28:57.205259Z"
}
}
],
"cvssMetricV2": [
{
"type": "Primary",
"source": "nvd@nist.gov",
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"accessVector": "NETWORK",
"vectorString": "AV:N/AC:L/Au:N/C:P/I:N/A:N",
"authentication": "NONE",
"integrityImpact": "NONE",
"accessComplexity": "LOW",
"availabilityImpact": "NONE",
"confidentialityImpact": "PARTIAL"
},
"acInsufInfo": false,
"impactScore": 2.9,
"baseSeverity": "MEDIUM",
"obtainAllPrivilege": false,
"exploitabilityScore": 10,
"obtainUserPrivilege": false,
"obtainOtherPrivilege": false,
"userInteractionRequired": false
}
],
"cvssMetricV31": [
{
"type": "Secondary",
"source": "secure@microsoft.com",
"cvssData": {
"scope": "UNCHANGED",
"version": "3.1",
"baseScore": 5.3,
"attackVector": "NETWORK",
"baseSeverity": "MEDIUM",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N",
"integrityImpact": "NONE",
"userInteraction": "NONE",
"attackComplexity": "LOW",
"availabilityImpact": "NONE",
"privilegesRequired": "NONE",
"confidentialityImpact": "LOW"
},
"impactScore": 1.4,
"exploitabilityScore": 3.9
},
{
"type": "Secondary",
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"cvssData": {
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"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
"integrityImpact": "NONE",
"userInteraction": "NONE",
"attackComplexity": "LOW",
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"confidentialityImpact": "HIGH"
},
"impactScore": 3.6,
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}
]
},
"affected": [
{
"source": "secure@microsoft.com",
"affectedData": [
{
"cpes": [
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],
"vendor": "Microsoft",
"product": "Windows Server 2019",
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"version": "10.0.0",
"lessThan": "10.0.17763.2237",
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"platforms": [
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},
{
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"product": "Windows Server 2019 (Server Core installation)",
"versions": [
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{
"cpes": [
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"vendor": "Microsoft",
"product": "Windows Server 2022",
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"platforms": [
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},
{
"cpes": [
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],
"vendor": "Microsoft",
"product": "Windows Server version 2004",
"versions": [
{
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"version": "10.0.0",
"lessThan": "10.0.19041.1288",
"versionType": "custom"
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"platforms": [
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},
{
"cpes": [
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"vendor": "Microsoft",
"product": "Windows Server version 20H2",
"versions": [
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"version": "10.0.0",
"lessThan": "10.0.19042.1288",
"versionType": "custom"
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],
"platforms": [
"x64-based Systems"
]
}
]
}
],
"published": "2021-10-13T01:15:09.890",
"references": [
{
"url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-40456",
"tags": [
"Patch",
"Vendor Advisory"
],
"source": "secure@microsoft.com"
},
{
"url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-40456",
"tags": [
"Patch",
"Vendor Advisory"
],
"source": "af854a3a-2127-422b-91ae-364da2661108"
}
],
"vulnStatus": "Modified",
"weaknesses": [
{
"type": "Primary",
"source": "nvd@nist.gov",
"description": [
{
"lang": "en",
"value": "NVD-CWE-noinfo"
}
]
},
{
"type": "Secondary",
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"description": [
{
"lang": "en",
"value": "CWE-863"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "Windows AD FS Security Feature Bypass Vulnerability"
},
{
"lang": "es",
"value": "Una vulnerabilidad de Omisión de la Funcionalidad de Seguridad de Windows AD FS"
}
],
"lastModified": "2026-06-17T04:06:57.370",
"configurations": [
{
"nodes": [
{
"negate": false,
"cpeMatch": [
{
"criteria": "cpe:2.3:o:microsoft:windows_server:20h2:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "1EAF6DBA-6E3A-4854-BFBF-B5DC36CE5929"
},
{
"criteria": "cpe:2.3:o:microsoft:windows_server_2019:-:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "DB79EE26-FC32-417D-A49C-A1A63165A968"
},
{
"criteria": "cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*",
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"matchCriteriaId": "1F0241B0-855A-489C-9AAE-68BC2556F24D"
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],
"operator": "OR"
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],
"sourceIdentifier": "secure@microsoft.com"
}