Evidence dossier

CVE-2021-34527

Windows Print Spooler Remote Code Execution Vulnerability

Exploited in the wild (CISA KEV since Nov 3, 2021). microsoft reports CVSS 3.1 8.8. EPSS estimates 99.8% exploit likelihood as of Oct 8, 2026.

82.0–95.1Priority evidence range

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

As of Oct 22, 2026

Normalized restatement

A remote code execution vulnerability exists when the Windows Print Spooler service improperly performs privileged file operations. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. UPDATE July 7, 2021: The security update for Windows Server 2012, Windows Server 2016 and Windows 10, Version 1607 have been released. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability. In addition to installing the updates, in order to secure your system, you must confirm that the following registry settings are set to 0 (zero) or are not defined (Note: These registry keys do not exist by default, and therefore are already at the secure setting.), also that your Group Policy setting are correct (see FAQ): HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint NoWarningNoElevationOnInstall = 0 (DWORD) or not defined (default setting) UpdatePromptSettings = 0 (DWORD) or not defined (default setting) Having NoWarningNoElevationOnInstall set to 1 makes your system vulnerable by design. UPDATE July 6, 2021: Microsoft has completed the investigation and has released security updates to address this vulnerability. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability. See also KB5005010: Restricting installation of new printer drivers after applying the July 6, 2021 updates. Note that the security updates released on and after July 6, 2021 contain protections for CVE-2021-1675 and the additional remote code execution exploit in the Windows Print Spooler service known as “PrintNightmare”, documented in CVE-2021-34527.

State: PUBLISHED
Published: Jul 2, 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 Print Spooler Remote Code Execution Vulnerability
Inspect raw assertion
Field
container
Value
Windows Print Spooler Remote Code Execution Vulnerability
Original evidence ↗
Source dateSep 1, 2026First observed by CASCASep 1, 2026
CISA KEV
Exploitation cataloged: Microsoft Windows Print Spooler Remote Code Execution Vulnerability
Inspect raw assertion
Field
observed_exploitation
Value
Microsoft Windows Print Spooler Remote Code Execution Vulnerability
Original evidence ↗
Source dateOct 8, 2026First observed by CASCAOct 9, 2026
FIRST EPSS
EPSS score: 99.79% probability · 99.96th percentile
Inspect raw assertion
Field
model_probability
Value
Probability 0.997920000000; percentile 0.999560000000
Original evidence ↗

ExploitationCatalog member

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

Exploit likelihood99.79%

FIRST EPSS · score date Oct 8, 2026 · 100th percentile · first observed Oct 9, 2026

SeverityCVSS 8.8

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 Print Spooler Remote Code Execution Vulnerability

Inspect raw assertion

Field: container
Value: Windows Print Spooler Remote Code Execution Vulnerability

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

CISA KEVOriginal assertion

Exploitation cataloged

Microsoft Windows Print Spooler Remote Code Execution Vulnerability

Inspect raw assertion

Field: observed_exploitation
Value: Microsoft Windows Print Spooler Remote Code Execution Vulnerability

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

FIRST EPSSOriginal assertion

EPSS score

99.79% probability · 99.96th percentile

Inspect raw assertion

Field: model_probability
Value: Probability 0.997920000000; percentile 0.999560000000

Source dateOct 8, 2026First observed by CASCAOct 9, 2026Original evidence ↗

Applicability

Cited product scope

Trace impact →

19Underlying assertions

17Canonical products

19Target 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

41 scope groups

microsoft · source assertedMicrosoftWindows 10 Version 1507Direct source scope

Affected: 10.0.10240.0 to before 10.0.10240.18969 (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": "10.0.10240.18969", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 1607Direct source scope

Affected: 10.0.14393.0 to before 10.0.14393.4470 (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": "10.0.14393.4470", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 1809Direct source scope

Affected: 10.0.17763.0 to before 10.0.17763.2029 (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": "10.0.17763.2029", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 1809Direct source scope

Affected: 10.0.0 to before 10.0.17763.2029 (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": "10.0.17763.2029", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 20H2Direct source scope

Affected: 10.0.0 to before 10.0.19042.1083 (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": "10.0.19042.1083", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 21H2Direct source scope

Affected: 10.0.19044.0 to before 10.0.19044.1415 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "10.0.19044.0", "lessThan": "10.0.19044.1415", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 10 Version 22H2Direct source scope

Affected: 10.0.19045.0 to before 10.0.19045.2251 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "10.0.19045.0", "lessThan": "10.0.19045.2251", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 11 version 21H2Direct source scope

Affected: 10.0.22000.0 to before 10.0.22000.318 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "10.0.22000.0", "lessThan": "10.0.22000.318", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 11 version 22H2Direct source scope

Affected: 10.0.22621.0 to before 10.0.22621.674 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "10.0.22621.0", "lessThan": "10.0.22621.674", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows 8.1Direct source scope

Affected: 6.3.0 to before 6.3.9600.20046 (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": "6.3.9600.20046", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2008 R2 Service Pack 1Direct source scope

Affected: 6.1.7601.0 to before 6.1.7601.25633 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "6.1.7601.0", "lessThan": "6.1.7601.25633", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2008 R2 Service Pack 1 (Server Core installation)Direct source scope

Affected: 6.1.7601.0 to before 6.1.7601.25633 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "6.1.7601.0", "lessThan": "6.1.7601.25633", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2008 Service Pack 2Direct source scope

Affected: 6.0.6003.0 to before 6.0.6003.21138 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "6.0.6003.0", "lessThan": "6.0.6003.21138", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2008 Service Pack 2 (Server Core installation)Direct source scope

Affected: 6.0.6003.0 to before 6.0.6003.21138 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "6.0.6003.0", "lessThan": "6.0.6003.21138", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2012Direct source scope

Affected: 6.2.9200.0 to before 6.2.9200.23383 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "6.2.9200.0", "lessThan": "6.2.9200.23383", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2012 R2Direct source scope

Affected: 6.3.9600.0 to before 6.3.9600.20046 (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": "6.3.9600.20046", "versionType": "custom"}]

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

Affected: 6.3.9600.0 to before 6.3.9600.20046 (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": "6.3.9600.20046", "versionType": "custom"}]

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

Affected: 6.2.9200.0 to before 6.2.9200.23383 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "6.2.9200.0", "lessThan": "6.2.9200.23383", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2016Direct source scope

Affected: 10.0.14393.0 to before 10.0.14393.4470 (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": "10.0.14393.4470", "versionType": "custom"}]

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

Affected: 10.0.14393.0 to before 10.0.14393.4470 (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": "10.0.14393.4470", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2019Direct source scope

Affected: 10.0.17763.0 to before 10.0.17763.2029 (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": "10.0.17763.2029", "versionType": "custom"}]

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

Affected: 10.0.17763.0 to before 10.0.17763.2029 (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": "10.0.17763.2029", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server 2022Direct source scope

Affected: 10.0.20348.0 to before 10.0.20348.230 (custom comparison)

Source-reported scope

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

Inspect raw assertion

[{"status": "affected", "version": "10.0.20348.0", "lessThan": "10.0.20348.230", "versionType": "custom"}]

microsoft · source assertedMicrosoftWindows Server version 20H2Direct source scope

Affected: 10.0.0 to before 10.0.19042.1083 (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": "10.0.19042.1083", "versionType": "custom"}]

NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_1507Vulnerable target · 1 assertions

Any version (unconstrained) (< 10.0.10240.18969)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 10.0.10240.18969
Match ID
8c882409-bb85-490b-9d50-571b16c0de86

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: 24
Mapping revision: cpe23-exact-mapping-v1
Observed cutoff: Oct 22, 2026

Retained assertion IDs

06bd3edf-6460-4d43-8725-a1026bbe6ccc111bae81-f881-4475-b44c-ef2a889655241b637eeb-5517-4526-821e-1a9305ac86bf1c4aa696-7cd7-4b68-8991-68fab3f835a821899c1f-1963-4c78-a43c-48edd330ebf622c7044a-6fbf-478f-8ec0-a361a6efa859248b2c16-e2fc-48be-8f90-b643c8f7051d2d78c5d3-2feb-4e43-a141-ee289a5e33d2359b626a-fa29-44f0-92e2-1548e6cb996e41766c3b-b112-4bac-8c17-d518b4e02bb453ce4983-bbea-472c-bd6a-7fc5a4bc7d3656136a17-93be-4d75-887f-702fea416ddd7caea62e-f147-40da-9556-8088a54da12a82d5255a-c58f-4f54-84b0-d2b43e17d46b8a1a8458-6d89-4f2f-b602-8ecdf0d81d688d589000-6afa-4774-9f29-27e5822d1ef69164ab8b-2486-4734-a224-9a13d4b22a9fb8e9c6d5-21a4-4576-a4b3-ae1f9bc2c6fdc13d4607-58cd-420b-b2c4-200df8d70e86c6a5af97-d9f1-45b8-adc1-f49bc4e0b38dc80b4175-b3a7-469c-9015-d6840fb7ef25da0ca746-200c-4f50-895a-584cde8ccdcff4009dd3-02ca-497c-b064-712c8a37c5ecf5d632eb-5eab-4d69-bee5-20437f6a5cb3

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: 17
Mapping revision: cpe23-exact-mapping-v1
Observed cutoff: Oct 22, 2026

Retained assertion IDs

07fc66ba-fc67-479c-9972-f52686ee7827139ed83a-23c7-4b4a-a164-652799af0744176ca6da-bfad-4ba1-ab1c-9916be7a784c236254c3-f9ae-4086-ac1f-b1067920326c2ab2dbfd-cbad-4dbb-99f2-6bd597a9849e2b01e6ba-fa6b-475e-939c-103dcc52a1595d12b3bb-2c74-4396-a674-b446dc9dd04466b32dfb-4b50-4f14-9b2a-bd30caccc5466c031e07-b7e4-43da-b297-978f98f9b0a179f81ea6-1a13-4745-a4dc-7ffb110ac8078d3362a4-f650-4537-a0f3-077d590ec56abed87d8f-07c3-4c0a-9b9d-a466cf94d69fc5fe527a-dace-45bf-b939-13d05214f666ca5c7ed3-9cf9-4327-b0e0-a7ee4a7efd4eccb77f71-1ae6-4b6b-be24-7f1094501bbdcd1c2c88-c859-4670-8aaf-f6070ff907d2d22ec6ef-7b0e-415f-954d-5fc40bc7a867

Assessments

CVSS by origin

9.0

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

8.8

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

8.8

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

8.8

microsoftCVSS 3.1 · role unknown · display onlyDirect record assessment retained outside normalized eligibilityCVSS:3.1/AV:N/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

8.8Priority eligible

microsoft

CVSS 3.1 · Primary · Original assertion · rank 1

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

Validation: Valid match
Recomputed: 8.8
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.