Security readout for executives and security teams
Plain-English summary
CVE-2021-1691 is a Microsoft Windows Hyper-V denial-of-service issue. A successful attack could disrupt availability of affected systems, which matters most where Hyper-V supports production workloads. The source bundle does not describe data theft, privilege escalation, or code execution.
Executive priority
Treat as high priority where Hyper-V supports business-critical workloads. It is not presented as actively exploited in the provided sources, but availability impact on virtualization infrastructure can create operational disruption.
Technical view
The CVSS 3.1 vector is 7.7 high: network attack vector, low complexity, low privileges required, no user interaction, changed scope, and high availability impact. Affected entries include Windows Server 20H2, Windows Server 1909/2004, and Windows 10 1909/2004 variants listed by Microsoft/NVD data.
Likely exposure
Exposure is most likely on organizations running Hyper-V on the affected Windows Server or Windows 10 versions listed in the source bundle. Prioritize production virtualization hosts and any administrative workstations with Hyper-V enabled.
Exploitation context
The bundle marks KEV as false and provides no cited evidence of active exploitation. CVSS indicates exploitation may be possible remotely with low privileges, but the public bundle does not include exploit mechanics, proof-of-concept status, or attack telemetry.
Researcher notes
Evidence is limited: the description is terse, no CWE is supplied, and the bundle names no workaround beyond Microsoft advisory references. Avoid inferring guest-to-host impact or exploit paths without vendor detail.
Mitigation direction
- Review the Microsoft Update Guide entry for applicable fixes.
- Apply relevant Microsoft security updates to affected Hyper-V systems.
- Prioritize production Hyper-V hosts before lower-impact workstations.
- Check Microsoft guidance for any environment-specific workaround details.
- Track exceptions where affected versions cannot be patched promptly.
Validation and detection
- Inventory Windows hosts running the affected versions listed in the bundle.
- Confirm whether Hyper-V is enabled on each affected host.
- Verify Microsoft security updates addressing CVE-2021-1691 are installed.
- Review virtualization monitoring for unexplained Hyper-V availability events.
- Document unpatched systems and planned remediation dates.
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.
CVE-2021-1691 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
- 7.7 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:U/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.
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:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:U/RL:O/RC:C3.14Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.7HighVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:U/RL:O/RC:C
Source materials
- CVE List V5 sourceCVE List V5
- Windows Hyper-V Denial of Service VulnerabilityCVE reference · vendor-advisory
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-1691CVE reference · x_refsource_MISC, x_transferred
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.