Exploitation evidence
Known exploited · CISA KEV listed
Added 2026-01-26. Ransomware campaign use: Unknown.
CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
CISA due date: 2026-02-16. This is the catalog’s deadline, not an assessment of your organization’s exposure.
KEV checked 13 Nov 2026, 00:20 Jerusalem · Original catalog ↗Reported products and versions
Microsoft / Microsoft 365 Apps for Enterprise
Default status: Not specified
- affected: 16.0.1 to < https://aka.ms/OfficeSecurityReleases (custom)
Microsoft / Microsoft Office 2016
Default status: Not specified
- affected: 16.0.0 to < 16.0.5539.1001 (custom)
Microsoft / Microsoft Office 2019
Default status: Not specified
- affected: 19.0.0 to < 16.0.10417.20095 (custom)
Microsoft / Microsoft Office LTSC 2021
Default status: Not specified
- affected: 16.0.1 to < https://aka.ms/OfficeSecurityReleases (custom)
Microsoft / Microsoft Office LTSC 2024
Default status: Not specified
- affected: 16.0.0 to < https://aka.ms/OfficeSecurityReleases (custom)
Fixes and workarounds
No explicit solution text in the downloaded CVE record. Consult the vendor advisory; unaffected version ranges are shown above as reported, not inferred as a patch recommendation.
Sources and related reporting
CVE Program record ↗ · Download tracked evidence as JSON
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerability
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerability
Observed change timeline
History begins when Egret first downloads each source. It is not the complete upstream CVE history.
12 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-12",
"epss": 0.70823,
"percentile": 0.99407
}10 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-10",
"epss": 0.70823,
"percentile": 0.99404
}09 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-09",
"epss": 0.70823,
"percentile": 0.99403
}08 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-08",
"epss": 0.70795,
"percentile": 0.99403
}07 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-07",
"epss": 0.70795,
"percentile": 0.99403
}06 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-06",
"epss": 0.70795,
"percentile": 0.99402
}06 Nov 2026, 06:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-05",
"epss": 0.70795,
"percentile": 0.99401
}04 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-04",
"epss": 0.70795,
"percentile": 0.994
}03 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-03",
"epss": 0.70795,
"percentile": 0.994
}03 Nov 2026, 12:20 Jerusalem · CVE Program record changed
Stored CNA snapshot at this observation.
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-21509",
"options": [
{
"Exploitation": "active"
},
{
"Automatable": "no"
},
{
"Technical Impact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-01-26T00:00:00+00:00",
"version": "2.0.3"
},
"type": "ssvc"
}
},
{
"other": {
"content": {
"dateAdded": "2026-01-26",
"reference": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509"
},
"type": "kev"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-06-25T03:55:21.534Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"references": [
{
"tags": [
"government-resource"
],
"url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509"
}
],
"title": "CISA ADP Vulnrichment"
},
{
"providerMetadata": {
"dateUpdated": "2026-02-10T14:57:48.648Z",
"orgId": "af854a3a-2127-422b-91ae-364da2661108",
"shortName": "CVE"
},
"references": [
{
"url": "https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerability"
},
{
"url": "https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerability"
}
],
"title": "CVE Program Container",
"x_generator": {
"engine": "ADPogram 0.0.1"
}
}
],
"cna": {
"affected": [
{
"platforms": [
"32-bit Systems",
"x64-based Systems"
],
"product": "Microsoft 365 Apps for Enterprise",
"vendor": "Microsoft",
"versions": [
{
"lessThan": "https://aka.ms/OfficeSecurityReleases",
"status": "affected",
"version": "16.0.1",
"versionType": "custom"
}
]
},
{
"platforms": [
"32-bit Systems",
"x64-based Systems"
],
"product": "Microsoft Office 2016",
"vendor": "Microsoft",
"versions": [
{
"lessThan": "16.0.5539.1001",
"status": "affected",
"version": "16.0.0",
"versionType": "custom"
}
]
},
{
"platforms": [
"32-bit Systems",
"x64-based Systems"
],
"product": "Microsoft Office 2019",
"vendor": "Microsoft",
"versions": [
{
"lessThan": "16.0.10417.20095",
"status": "affected",
"version": "19.0.0",
"versionType": "custom"
}
]
},
{
"platforms": [
"32-bit Systems",
"x64-based Systems"
],
"product": "Microsoft Office LTSC 2021",
"vendor": "Microsoft",
"versions": [
{
"lessThan": "https://aka.ms/OfficeSecurityReleases",
"status": "affected",
"version": "16.0.1",
"versionType": "custom"
}
]
},
{
"platforms": [
"32-bit Systems",
"x64-based Systems"
],
"product": "Microsoft Office LTSC 2024",
"vendor": "Microsoft",
"versions": [
{
"lessThan": "https://aka.ms/OfficeSecurityReleases",
"status": "affected",
"version": "16.0.0",
"versionType": "custom"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:a:microsoft:office_2019:*:*:*:*:*:*:*:*",
"versionEndExcluding": "16.0.10417.20095",
"versionStartIncluding": "19.0.0",
"vulnerable": true
},
{
"criteria": "cpe:2.3:a:microsoft:365_apps:*:*:*:*:enterprise:*:*:*",
"versionEndExcluding": "https://aka.ms/OfficeSecurityReleases",
"versionStartIncluding": "16.0.1",
"vulnerable": true
},
{
"criteria": "cpe:2.3:a:microsoft:office_2021:*:*:*:*:long_term_servicing_channel:*:*:*",
"versionEndExcluding": "https://aka.ms/OfficeSecurityReleases",
"versionStartIncluding": "16.0.1",
"vulnerable": true
},
{
"criteria": "cpe:2.3:a:microsoft:office_2024:*:*:*:*:long_term_servicing_channel:*:*:*",
"versionEndExcluding": "https://aka.ms/OfficeSecurityReleases",
"versionStartIncluding": "16.0.0",
"vulnerable": true
},
{
"criteria": "cpe:2.3:a:microsoft:office_2016:*:*:*:*:*:*:x86:*",
"versionEndExcluding": "16.0.5539.1001",
"versionStartIncluding": "16.0.0",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
],
"datePublic": "2026-01-26T16:00:00.000Z",
"descriptions": [
{
"lang": "en-US",
"value": "Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C",
"version": "3.1"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en-US",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-807",
"description": "CWE-807: Reliance on Untrusted Inputs in a Security Decision",
"lang": "en-US",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-07-30T20:47:35.007Z",
"orgId": "f38d906d-7342-40ea-92c1-6c4a2c6478c8",
"shortName": "microsoft"
},
"references": [
{
"name": "Microsoft Office Security Feature Bypass Vulnerability",
"tags": [
"vendor-advisory",
"patch"
],
"url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509"
}
],
"title": "Microsoft Office Security Feature Bypass Vulnerability"
}
},
"cveMetadata": {
"assignerOrgId": "f38d906d-7342-40ea-92c1-6c4a2c6478c8",
"assignerShortName": "microsoft",
"cveId": "CVE-2026-21509",
"datePublished": "2026-01-26T17:06:35.512Z",
"dateReserved": "2025-12-30T18:10:54.844Z",
"dateUpdated": "2026-07-30T20:47:35.007Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}03 Nov 2026, 02:22 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-02",
"epss": 0.70795,
"percentile": 0.99398
}03 Nov 2026, 02:22 Jerusalem · CISA KEV status changed
Stored KEV snapshot at this observation.
{
"cveID": "CVE-2026-21509",
"cwes": [
"CWE-807"
],
"dateAdded": "2026-01-26",
"dueDate": "2026-02-16",
"forensicTriage": "No",
"knownRansomwareCampaignUse": "Unknown",
"notes": "Please adhere to Microsoft’s recommended guidelines to address this vulnerability. Implement all final mitigations provided by the vendor for Office 2021, and apply the interim corresponding mitigations for Office 2016 and Office 2019 until the final patch becomes available. For more information please see: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509 ; https://nvd.nist.gov/vuln/detail/CVE-2026-21509",
"product": "Office",
"requiredAction": "Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.",
"shortDescription": "Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.",
"vendorProject": "Microsoft",
"vulnerabilityName": "Microsoft Office Security Feature Bypass Vulnerability"
}