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Full vulnerability report · 2021
CVE-2021-31956High confidence

Microsoft Windows NTFS Privilege Escalation Vulnerability

Microsoft · Windows

7.8HighCVSS 3.1
Recommended action
Patch now

CISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Critical, raised one band.upgradedsince 3 Nov 2021

Evidence used

  • CISA confirms exploitation in the wild.
  • Exploitation requires an existing local or physical foothold with privileges.
  • EPSS is 22.27% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict local access and enforce least privilege on affected hosts.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs Microsoft Windows and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-18829

CISA KEV mirrored by ENISA

Windows NTFS Elevation of Privilege Vulnerability

EUVD state
Present in the current official mapping
Known exploitation
Recorded by ENISA since 3 Nov 2021. Evidence sources: cisa_kev.
ENISA score
7.8 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch now

CISA confirms exploitation in the wild and lists 2021-11-17 as the remediation due date.

Patch available
01

What, why and how

Microsoft Windows New Technology File System (NTFS) contains an unspecified vulnerability that allows attackers to escalate privileges via a specially crafted application.

What

Microsoft Windows New Technology File System (NTFS) contains an unspecified vulnerability that allows attackers to escalate privileges via a specially crafted application.

Why

The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

Microsoft Windows New Technology File System (NTFS) contains an unspecified vulnerability that allows attackers to escalate privileges via a specially crafted application.

Why

The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Confirmed in the wild

CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2021-11-03.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
local access → Integer Underflow (Wrap or Wraparound) → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Local
Privileges required
Low: a basic authenticated account is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-191 ↗

CWE-191: Integer Underflow (Wrap or Wraparound). The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
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

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
CWE-191CISA KEV
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2021-18829Known-exploited evidence recorded

Windows NTFS Elevation of Privilege Vulnerability

Official EUVD record ↗
Canadian Centre for Cyber Security · English · AV21-273Microsoft security advisory – June 2021 monthly rollup

On 8 June 2021 Microsoft published Security Updates to address vulnerabilities in multiple products. Included were critical updates for the following: Exploitation of some of these vulnerabilities could allow an actor to execute code remotely or corrupt memory.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20210609Security Bulletin 09 Jun 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 09 Jun 2021, published on 9 June 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-448Multiples vulnérabilités dans Microsoft Windows

rd?id=CVE-2021-1675 Référence CVE CVE-2021-26414 https://www.cve.org/CVERecord?id=CVE-2021-26414 Référence CVE CVE-2021-31199 https://www.cve.org/CVERecord?id=CVE-2021-31199 Référence CVE CVE-2021-31201 https://www.cve.org/CVERecord?id=CVE-2021-31201 Référence CVE CVE-2021-31951 https://www.cve.org/CVERecord?id=CVE-2021-31951 Référence CVE CVE-2021-31952 https://www.cve.org/CVERecord?id=CVE-2021-31952 Référence CVE CVE-2021-31953 https://www.cve.org/CVERecord?id=CVE-2021-31953 Référence CVE CVE-2021-31954 https://www.cve.org/CVERecord?id=CVE-2021-31954 Référence CVE CVE-2021-31955 https://www.cve.org/CVERecord?id=CVE-2021-31955 Référence CVE CVE-2021-31956 https://www.cve.org/CVERecord?id=CVE-2021-31956 Référence CVE CVE-2021-31958 https://www.cve.org/CVERecord?id=CVE-2021-31958 Référence CVE CVE-2021-31959 https://www.cve.org/CVERecord?id=CVE-2021-31959 Référence CVE CVE-2021-31960 https://www.cve.org/CVERecord?id=CVE-2021-31960 Référence CVE CVE-2021-31962 https://www.cve.org/CVERecord?id=CVE-2021-31962 Référence CVE CVE-2021-31968 https://www.cve.org/CVERecord?id=CVE-2021-31968 Référence CVE CVE-2021-31969 https://www.cve.org/CVERecord?id=CVE-2021-31969 Référence CVE CVE-2021-31970 https://www.cve.org/CVERecord?id=CVE-2021-31970 Référence CVE CVE-2021-31971 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-001934複数の Microsoft Windows 製品における権限を昇格される脆弱性

複数の Microsoft Windows 製品には、Windows NTFS に不備があるため、権限を昇格される脆弱性が存在します。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-5318MS 6월 보안 위협에 따른 정기 보안 업데이트 권고

L Platform CVE-2021-31971 Windows HTML 플랫폼 보안 기능 우회 취약성 Windows Installer CVE-2021-31973 Windows GPSVC 권한 상승 취약성 Windows Kerberos CVE-2021-31962 Kerberos AppContainer 보안 기능 우회 취약성 Windows Kernel CVE-2021-31955 Windows 커널 정보 유출 취약성 Windows Kernel CVE-2021-31951 Windows 커널 권한 상승 취약성 Windows Kernel-Mode Drivers CVE-2021-31952 Windows 커널 모드 드라이버 권한 상승 취약성 Windows MSHTML Platform CVE-2021-33742 Windows MSHTML Platform Remote Code Execution Vulnerability Windows Network File System CVE-2021-31976 NFS용 서버 정보 유출 취약성 Windows Network File System CVE-2021-31975 NFS용 서버 정보 유출 취약성 Windows Network File System CVE-2021-31974 NFS용 서버 서비스 거부 취약성 Windows NTFS CVE-2021-31956 Windows NTFS 권한 상승 취약성 Windows NTLM CVE-2021-31958 Windows NTLM 권한 상승 취약성 Windows Print Spooler Components CVE-2021-1675 Windows 인쇄 스풀러 권한 상승 취약성 Windows Remote Desktop CVE-2021-31968 Windows 원격 데스크톱 서비스 서비스 거부 취약성 Windows TCP/IP CVE-2021-31970 Windows TCP/IP 드라이버 보안 기능 우회 취약성 ##### □ 작성 : 침해사고분석단 취약점분석팀

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Fixed
An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 8 Jun 2021 · Last source change 12 Jan 2026, 20:27 UTC · CWE-191 · Integer Underflow (Wrap or Wraparound)

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-18829
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceCISA ADP
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    10.0.0 < 10.0.17763.1999; 10.0.0 < 10.0.18363.1621; 10.0.0 < 10.0.19043.1052; 10.0.0 < 10.0.19041.1052; 10.0.0 < 10.0.19042.1052 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    After
    Windows 10 Version 1809: 10.0.0 < 10.0.17763.1999; Windows Server 2019: 10.0.0 < 10.0.17763.1999; Windows Server 2019 (Server Core installation): 10.0.0 < 10.0.17763.1999; Windows 10 Version 1909: 10.0.0 < 10.0.18363.1621; Windows 10 Version 21H1: 10.0.0 < 10.0.19043.1052; Windows 10 Version 2004: 10.0.0 < 10.0.19041.1052; Windows Server version 2004: 10.0.0 < 10.0.19041.1052; Windows 10 Version 20H2: 10.0.0 < 10.0.19042.1052; Windows Server version 20H2: 10.0.0 < 10.0.19042.1052; Windows 10 Version 1507: 10.0.0 < 10.0.10240.18967; Windows 10 Version 1607: 10.0.0 < 10.0.14393.4467; Windows Server 2016: 10.0.0 < 10.0.14393.4467; Windows Server 2016 (Server Core installation): 10.0.0 < 10.0.14393.4467; Windows 7: 6.1.0 < 6.1.7601.25632; Windows 7 Service Pack 1: 6.1.0 < 6.1.7601.25632; Windows 8.1: 6.3.0 < 6.3.9600.20045, 6.3.0 < 6.3.9600.20044; Windows Server 2008 Service Pack 2: 6.0.0 < 6.0.6003.21137; Windows Server 2008 Service Pack 2 (Server Core installation): 6.0.0 < 6.0.6003.21137; Windows Server 2008 Service Pack 2: 6.0.0 < 6.0.6003.21137; Windows Server 2008 R2 Service Pack 1: 6.1.0 < 6.1.7601.25632; Windows Server 2008 R2 Service Pack 1 (Server Core installation): 6.0.0 < 6.1.7601.25632; Windows Server 2012: 6.2.0 < 6.2.9200.23372; Windows Server 2012 (Server Core installation): 6.2.0 < 6.2.9200.23372; Windows Server 2012 R2: 6.3.0 < 6.3.9600.20045, 6.3.0 < 6.3.9600.20044; Windows Server 2012 R2 (Server Core installation): 6.3.0 < 6.3.9600.20045, 6.3.0 < 6.3.9600.20044 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Added to CISA KEV
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-18829↗CISA KEV record↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-31956 · cve.blacktree.nl