Evidence dossier

CVE-2021-33771

Windows Kernel Elevation of Privilege Vulnerability

Exploited in the wild (CISA KEV since Nov 3, 2021). microsoft reports CVSS 3.1 7.8. EPSS estimates 10.2% exploit likelihood as of Oct 22, 2026.

65.9–78.4Priority evidence range

Evidence through Oct 22, 2026, 6:07 PM UTC

As of Oct 22, 2026

Normalized restatement

Windows Kernel Elevation of Privilege Vulnerability

State: PUBLISHED
Published: Jul 14, 2021
Updated: Aug 10, 2026
Evidence coverage: 85%

Evidence chronology

What was known when

Download this view's receipt →

Source dateSource date omittedFirst observed by CASCAAug 10, 2026
CISA-ADP
Record text: CISA ADP Vulnrichment
Inspect raw assertion
Field
container
Value
CISA ADP Vulnrichment
Original evidence ↗
Source dateSource date omittedFirst observed by CASCAAug 10, 2026
CVE Program
Record text: CVE Program Container
Inspect raw assertion
Field
container
Value
CVE Program Container
Original evidence ↗
Source dateSource date omittedFirst observed by CASCAAug 10, 2026
microsoft
Record text: Windows Kernel Elevation of Privilege Vulnerability
Inspect raw assertion
Field
container
Value
Windows Kernel Elevation of Privilege Vulnerability
Original evidence ↗
Source dateSep 1, 2026First observed by CASCASep 1, 2026
CISA KEV
Exploitation cataloged: Microsoft Windows Kernel Privilege Escalation Vulnerability
Inspect raw assertion
Field
observed_exploitation
Value
Microsoft Windows Kernel Privilege Escalation Vulnerability
Original evidence ↗
Source dateOct 22, 2026First observed by CASCAOct 22, 2026
FIRST EPSS
EPSS score: 10.17% probability · 95.66th percentile
Inspect raw assertion
Field
model_probability
Value
Probability 0.101720000000; percentile 0.956570000000
Original evidence ↗

ExploitationCatalog member

CISA KEV · catalog date Nov 3, 2021 · first observed Sep 1, 2026

Exploit likelihood10.17%

FIRST EPSS · score date Oct 22, 2026 · 95.7th percentile · first observed Oct 22, 2026

SeverityCVSS 7.8

microsoft · CVSS 3.1 · first observed Aug 10, 2026 · same-version scores align in this snapshot

Evidence detail

Source limits and decisions

Why each evidence state has this value

casca-unknown-reasons-v1

Exploitation statusLast verified source snapshot retained

The last verified source boundary remains in force for this claim.

Revision: evidence-policy-v1.1.0
Cutoff: Oct 22, 2026
Resolution: Review source contract

Exploit likelihoodEvidence supported

Eligible evidence is present for this bounded claim.

Revision: evidence-policy-v1.1.0
Cutoff: Oct 22, 2026
Resolution: None

Severity assessmentEvidence supported

Eligible evidence is present for this bounded claim.

Revision: casca-direct-cvss-eligibility-v1
Cutoff: Oct 22, 2026
Resolution: None

Affected productsSource-reported scope

The cited source assertion is retained while canonical product linkage remains open.

Revision: casca-factor-d-obligations-v1
Cutoff: Oct 22, 2026
Resolution: Resolve identity

Source comparison

Who said what

CISA-ADPIndependent enrichment

Record text

CISA ADP Vulnrichment

Inspect raw assertion

Field: container
Value: CISA ADP Vulnrichment

Source dateSource date omittedFirst observed by CASCAAug 10, 2026Original evidence ↗

CVE ProgramDerivative copy

Record text

CVE Program Container

Inspect raw assertion

Field: container
Value: CVE Program Container

Source dateSource date omittedFirst observed by CASCAAug 10, 2026Original evidence ↗

microsoftOriginal assertion

Record text

Windows Kernel Elevation of Privilege Vulnerability

Inspect raw assertion

Field: container
Value: Windows Kernel Elevation of Privilege Vulnerability

Source dateSource date omittedFirst observed by CASCAAug 10, 2026Original evidence ↗

CISA KEVOriginal assertion

Exploitation cataloged

Microsoft Windows Kernel Privilege Escalation Vulnerability

Inspect raw assertion

Field: observed_exploitation
Value: Microsoft Windows Kernel Privilege Escalation Vulnerability

Source dateSep 1, 2026First observed by CASCASep 1, 2026Original evidence ↗

FIRST EPSSOriginal assertion

EPSS score

10.17% probability · 95.66th percentile

Inspect raw assertion

Field: model_probability
Value: Probability 0.101720000000; percentile 0.956570000000

Source dateOct 22, 2026First observed by CASCAOct 22, 2026Original evidence ↗

Applicability

Cited product scope

Trace impact →

16Underlying assertions

15Canonical products

16Target assertions

0Constraint assertions

Grouped from 1 configuration nodes in this exact snapshot. Visual grouping is navigational; asset exposure and root cause require cited evidence.

Identity source boundaries

Cpe dictionary1,775,266 records · observed through 2026-07-21T06:45:29.809Z27d65b0f-b718-4b4f-bb79-c47c68d09dfa
Cpe match643,502 records · observed through 2026-07-21T08:13:17.697Z955dae73-7302-438b-aee1-058d7cc5d48e

Search scopeRoleOfficial link state

32 scope groups

microsoft · source assertedMicrosoftWindows 10 Version 1507Direct source scope

Affected: 10.0.10240.0 to before 10.0.10240.19003 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.10240.0", "lessThan": "10.0.10240.19003", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 1607Direct source scope

Affected: 10.0.14393.0 to before 10.0.14393.4530 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.14393.0", "lessThan": "10.0.14393.4530", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 1809Direct source scope

Affected: 10.0.17763.0 to before 10.0.17763.2061 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.17763.0", "lessThan": "10.0.17763.2061", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 1809Direct source scope

Affected: 10.0.0 to before 10.0.17763.2061 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.17763.2061", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 1909Direct source scope

Affected: 10.0.0 to before 10.0.18363.1679 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.18363.1679", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 2004Direct source scope

Affected: 10.0.0 to before 10.0.19041.1110 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19041.1110", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 20H2Direct source scope

Affected: 10.0.0 to before 10.0.19042.1110 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19042.1110", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 21H1Direct source scope

Affected: 10.0.0 to before 10.0.19043.1110 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19043.1110", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 8.1Direct source scope

Affected: 6.3.0 to before 6.3.9600.20069 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "6.3.0", "lessThan": "6.3.9600.20069", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2012 R2Direct source scope

Affected: 6.3.9600.0 to before 6.3.9600.20069 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "6.3.9600.0", "lessThan": "6.3.9600.20069", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2012 R2 (Server Core installation)Direct source scope

Affected: 6.3.9600.0 to before 6.3.9600.20069 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "6.3.9600.0", "lessThan": "6.3.9600.20069", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2016Direct source scope

Affected: 10.0.14393.0 to before 10.0.14393.4530 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.14393.0", "lessThan": "10.0.14393.4530", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2016 (Server Core installation)Direct source scope

Affected: 10.0.14393.0 to before 10.0.14393.4530 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.14393.0", "lessThan": "10.0.14393.4530", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2019Direct source scope

Affected: 10.0.17763.0 to before 10.0.17763.2061 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.17763.0", "lessThan": "10.0.17763.2061", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2019 (Server Core installation)Direct source scope

Affected: 10.0.17763.0 to before 10.0.17763.2061 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.17763.0", "lessThan": "10.0.17763.2061", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server version 2004Direct source scope

Affected: 10.0.0 to before 10.0.19041.1110 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19041.1110", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server version 20H2Direct source scope

Affected: 10.0.0 to before 10.0.19042.1110 (custom comparison)

Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion

[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19042.1110", "versionType": "custom"}]

NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_1507Vulnerable target · 1 assertions

Any version (unconstrained) (< 10.0.10240.19003)Canonical identity product-9851bd571b8ab08bca589cd73710badfef557d036f0fb7707f694f1c9f597cb4Linked exact

Scope supported

Inspect raw assertion

cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*
Official link
Linked exact
Role
Vulnerable target
Configuration
0 · node/0 · match 0
Logic
OR
Version bounds
through excluding 10.0.10240.19003
Match ID
0c51cd3a-e78b-4a0d-8716-4f2c0a79ed68

NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_1607Vulnerable target · 1 assertions

Any version (unconstrained) (< 10.0.14393.4530)Canonical identity product-740fec3e9838b5eabe76ebe27e4d0d7a4cb2e0ef7e13923300d3d0b51e3fce1cLinked exact

Scope supported

Inspect raw assertion

cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:*:*
Official link
Linked exact
Role
Vulnerable target
Configuration
0 · node/0 · match 1
Logic
OR
Version bounds
through excluding 10.0.14393.4530
Match ID
9eebf8ac-ab6e-4f62-811a-0e53721c78f5

NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_1809Vulnerable target · 1 assertions

Any version (unconstrained) (< 10.0.17763.2061)Canonical identity product-a3084138383423221f61594e86f5b295e5e254acd7ae5284f45e0877a084db43Linked exact

Scope supported

Inspect raw assertion

cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:*:*
Official link
Linked exact
Role
Vulnerable target
Configuration
0 · node/0 · match 2
Logic
OR
Version bounds
through excluding 10.0.17763.2061
Match ID
5baabe12-c0e8-4e34-9efe-18dd50c54b1d

NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_1909Vulnerable target · 1 assertions

Any version (unconstrained) (< 10.0.18363.1679)Canonical identity product-ef5324dcc791e4e872d6c2be0aefa1d7687ca82c3b4ac5d1f72c76cce8395218Linked exact

Scope supported

Inspect raw assertion

cpe:2.3:o:microsoft:windows_10_1909:*:*:*:*:*:*:*:*
Official link
Linked exact
Role
Vulnerable target
Configuration
0 · node/0 · match 3
Logic
OR
Version bounds
through excluding 10.0.18363.1679
Match ID
1c9e359b-5719-48b1-babb-618744c73388

NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_2004Vulnerable target · 1 assertions

Any version (unconstrained) (< 10.0.19041.1110)Canonical identity product-9b245936275be71b526838fc72ea633d195b35bdd9dfc31bb6df51e7700edeccLinked exact

Scope supported

Inspect raw assertion

cpe:2.3:o:microsoft:windows_10_2004:*:*:*:*:*:*:*:*
Official link
Linked exact
Role
Vulnerable target
Configuration
0 · node/0 · match 4
Logic
OR
Version bounds
through excluding 10.0.19041.1110
Match ID
307c13cf-563b-46d1-9f2e-227ab9c40720

NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_20h2Vulnerable target · 1 assertions

Any version (unconstrained) (< 10.0.19042.1110)Canonical identity product-55e90faed8848f3d316cf702d119e83086b6dc5a963d9947a7df1c589f50346dLinked exact

Scope supported

Inspect raw assertion

cpe:2.3:o:microsoft:windows_10_20h2:*:*:*:*:*:*:*:*
Official link
Linked exact
Role
Vulnerable target
Configuration
0 · node/0 · match 5
Logic
OR
Version bounds
through excluding 10.0.19042.1110
Match ID
9aec53c7-c1cb-4ffb-8069-27604fb50f0b

NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_21h1Vulnerable target · 1 assertions

Any version (unconstrained) (< 10.0.19043.1110)Canonical identity product-e0c6c3f5c5e95b5b83fbbf719a7de2471749e1ca250bebf19bc7898a937a00edLinked exact

Scope supported

Inspect raw assertion

cpe:2.3:o:microsoft:windows_10_21h1:*:*:*:*:*:*:*:*
Official link
Linked exact
Role
Vulnerable target
Configuration
0 · node/0 · match 6
Logic
OR
Version bounds
through excluding 10.0.19043.1110
Match ID
765ba052-1b41-4cd3-98e6-f3750e0466e5

NVD CPE · OPERATING SYSTEMmicrosoftwindows_8.1Vulnerable target · 1 assertions

Version not applicableCanonical identity product-7e46de82012029583622f69d79b86bc210b5bd25b8cb3bb4468936702b23c4b0Linked exact

Scope supported

Inspect raw assertion

cpe:2.3:o:microsoft:windows_8.1:-:*:*:*:*:*:*:*
Official link
Linked exact
Role
Vulnerable target
Configuration
0 · node/0 · match 7
Logic
OR
Version bounds
No explicit bounds
Match ID
e93068db-549b-45ab-8e5c-00eb5d8b5cf8

Affected-product evidence

Accepted scope and product mapping

0 canonical links · 2 source-reported links

Source-reported scopeSource-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Vendor specified only by source · Product specified only by source

Source class: Direct cve affected
Assertions: 17
Mapping revision: cpe23-exact-mapping-v1
Observed cutoff: Oct 22, 2026

Retained assertion IDs

0d059b4a-deb6-42b6-b6af-c82f395805c311b8dad8-02aa-44d0-ad4b-329ed94cf6a5147df16f-ce67-4ac8-b4ed-74126f5414a0156de282-294c-458b-b96e-61d7da2d99d119863eef-f6e5-4d2f-b2be-4a89f96da1711a1139b7-3468-4a97-82a6-bf72b0686c093ab61755-84fa-4a9b-8bc8-d8fc161fabca42ad5740-c1b8-4450-acb8-f9ec5a3b3579495f0f4d-3550-478a-af83-1ca0a17bc2e2756fa7ea-0f4c-46c2-9c1b-1fefac57b5808a02d15d-3854-401a-9d3c-3915d5feab409190304f-8902-428c-a85e-8b2e53a5fb7cadd52939-32e0-4666-ba3d-c6ce2dea3fd4be8af101-617e-4217-bfb3-11df4af11e52ccc9bdef-a122-4d25-9e24-005046512f87fddc3500-279c-4a04-9b59-d14a75be63fcfe48f4e1-7691-4e27-8fe3-0d7d2fe563a4

Source-reported scopeSource-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Vendor specified only by source · Product specified only by source

Source class: Nvd cpe vulnerable target
Assertions: 14
Mapping revision: cpe23-exact-mapping-v1
Observed cutoff: Oct 22, 2026

Retained assertion IDs

183f3d53-5759-4c87-a1f5-8bf20d962bc82045146f-acf3-4539-86c9-0a0ce449f72f314558b0-ac45-4733-a45e-4c2c35678c8e3daa3716-aa37-4a29-9e06-27ad1463000f571229c2-a943-4478-8645-d518f0887a3e677161ea-24fc-4b6c-9e86-9f4d0e1b8326936d8d37-3fe8-4d44-ae00-9e82b55cda489e12788e-d8fe-40bb-ba64-6562c8dfd397a08bfc6e-95a9-4fb7-93d3-b3d9808b5db2bbfdb009-fa3d-41e2-892f-15c14c451134c6ac31a8-4fe5-4700-8236-a94d72030be8d35ab6f6-432b-430d-9e92-e1b9294e4014e8a9a157-de79-4827-8df1-920a5129e63ffdd94ff4-675f-4c2f-accc-fce3b9907fa8

Assessments

CVSS by origin

7.2

NVDCVSS 2.0 · role Primary · priority eligiblevalid_matchAV:L/AC:L/Au:N/C:C/I:C/A:C

7.8

NVDCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

7.8

secure@microsoft.comCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

7.8

microsoftCVSS 3.1 · role unknown · display onlyDirect record assessment retained outside normalized eligibilityCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

Direct CVE/CNA normalized decisions

7.8Priority eligible

microsoft

CVSS 3.1 · Primary · Original assertion · rank 1

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

Validation: Valid match
Recomputed: 7.8
Decision reason: Evidence supported
Policy: casca-direct-cvss-eligibility-v1

Assessments are retained side by side under closed precedence. Cascade never averages CVSS.

Evidence boundaries

KEV membership is authoritative for the catalog, not proof of exposure in any environment.
EPSS is a dated model probability and not an individual-environment prediction.
Affected or fixed status applies only to the exact cited product and version scope; remaining scope stays source-scoped.
NVD-carried upstream facts remain derivative; independent corroboration requires a separately authored source.
Only NVD metrics validated under the generation-bound calculator are Public Priority eligible; direct CVE record metrics remain display-only.
NVD CVSS source eligibility is closed: NVD-authored, exact record-source, or registered same-CVE container origin; unmapped sources remain display-only.
Core replay supports the active and immediately prior generation; retrospective valid-at replay is deferred.
OSV aggregation and OSV-converted NVD material are not independent corroboration.
Red Hat facts are vendor assertions for the exact supplied products.
Nonmembership and not-yet-observed states are not proof of safety.