Security readout for executives and security teams
Plain-English summary
CVE-2021-31191 is a Windows information disclosure flaw in the Projected File System filter driver. It requires local access with low privileges, so it is not a remote break-in by itself. The main business risk is sensitive data exposure on affected Windows endpoints or servers that have not received Microsoft’s fix.
Executive priority
Treat as a moderate-priority patching item. It is not presented as actively exploited or remotely exploitable in the supplied sources, but it can increase confidentiality risk on compromised or multi-user Windows systems.
Technical view
The CVSS vector is 5.5: local attack vector, low complexity, low privileges required, no user interaction, unchanged scope, high confidentiality impact, and no integrity or availability impact. Affected platforms include listed Windows 10 and Windows Server versions from 1803 through 20H2 and Server 2019 variants.
Likely exposure
Exposure is limited to affected Windows 10 and Windows Server systems listed in the source bundle, especially older builds around 1803, 1809, 1909, 2004, and 20H2. Organizations with strong patch management are less likely to remain exposed.
Exploitation context
The source bundle marks this CVE as not in CISA KEV and provides no cited evidence of active exploitation. The local, low-privilege requirement makes it more relevant after initial access or on shared systems than as an internet-facing entry point.
Researcher notes
The public details provided are sparse: no CWE is listed and no exploitation narrative is included. Validation should focus on affected build identification, patch state, and whether Projected File System-related exposure matters in local threat scenarios.
Mitigation direction
- Apply Microsoft guidance and security updates for CVE-2021-31191.
- Prioritize unsupported or older affected Windows builds for remediation review.
- Reduce local user privilege where possible on affected systems.
- Monitor Microsoft advisories for any revised mitigation or exploitability details.
Validation and detection
- Inventory Windows versions and builds against the affected product list.
- Confirm relevant Microsoft security updates are installed on affected systems.
- Review vulnerability scanner findings for CVE-2021-31191 on endpoints and servers.
- Check whether legacy Windows Server Core installations remain in service.
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-2021-31191 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
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/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:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C
Source materials
- CVE List V5 sourceCVE List V5
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31191CVE reference · x_refsource_MISC
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.