Security readout for executives and security teams
Plain-English summary
This Windows kernel flaw lets a user who already has limited local access gain higher privileges, potentially taking full control of an affected device. It is high severity and appears in CISA’s Known Exploited Vulnerabilities catalog, so exposed systems should be treated as urgent remediation targets.
Executive priority
Prioritize remediation promptly because exploitation is documented through CISA KEV and successful abuse can provide system-level impact after initial access. Focus first on exposed endpoints, shared systems, and servers where a low-privileged foothold could reach sensitive data or administrative infrastructure.
Technical view
CVE-2021-33771 is a local Windows kernel elevation-of-privilege vulnerability rated CVSS 3.1 7.8. Exploitation requires low privileges, has low attack complexity, needs no user interaction, and can compromise confidentiality, integrity, and availability. The supplied sources do not identify a CWE or explain the underlying kernel defect.
Likely exposure
Exposure includes listed Windows 8.1, Windows 10 releases from 1507 through 21H1, and Windows Server 2012 R2 through 20H2, including specified Server Core installations, when the applicable Microsoft security update is absent. Internet exposure is not required, but an attacker needs local low-privileged access.
Exploitation context
Active exploitation is supported by this CVE’s inclusion in CISA’s Known Exploited Vulnerabilities catalog. The supplied evidence does not identify observed campaigns, malware, exploitation frequency, affected organizations, or a public proof of concept. Treat it primarily as a privilege-escalation step that could deepen an existing endpoint compromise.
Researcher notes
The evidence establishes local attack vector, low complexity, low required privileges, no user interaction, high impact, vendor remediation, and KEV status. It does not provide root-cause details, affected kernel components, exploit mechanics, patch identifiers, detection signatures, or campaign attribution. Product-specific applicability should be confirmed against Microsoft’s advisory.
Mitigation direction
- Apply the applicable Microsoft security update from the vendor advisory.
- Prioritize affected systems where untrusted or compromised users can obtain local access.
- Restrict unnecessary local accounts and privileges while patching is underway.
- Check current Microsoft guidance for product-specific servicing and support requirements.
Validation and detection
- Inventory systems running the listed Windows client and server releases.
- Verify the applicable Microsoft security update is installed on each affected system.
- Confirm update deployment succeeded and systems completed any required restart.
- Review endpoint telemetry for suspicious privilege escalation around previously unpatched hosts.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
Privilege behavior lookup
The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-33771 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: 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
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C1.85.9microsoftVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: 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
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- Added to KEVCISA-ADP
CISA Known Exploited Vulnerabilities metadata lists this CVE as known exploited.
- ADP timelineCISA-ADP
CVE-2021-33771 added to CISA KEV
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2021-11-03T00:00:00.000Z: CVE-2021-33771 added to CISA KEV
Source materials
- CVE List V5 sourceCVE List V5
- Windows Kernel Elevation of Privilege VulnerabilityCVE reference, microsoft · vendor-advisory, patch
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33771CVE reference, CVE · x_refsource_MISC, x_transferred
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33771CVE reference, CISA-ADP · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.