Security readout for executives and security teams
Plain-English summary
This flaw lets an attacker bypass a Windows SMB client security control and potentially expose sensitive information. The sources rate it medium severity, with high confidentiality impact, but exploitation requires user interaction and no active exploitation is cited.
Executive priority
Treat this as routine-to-priority patching, not an emergency response item, unless exposed systems are unpatched and handle sensitive data. The main business concern is confidentiality loss, not service outage.
Technical view
CVE-2021-31205 is a Windows SMB Client security feature bypass. The CVSS 3.1 vector is AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N, indicating remote reachability, low complexity, no privileges, required user interaction, and confidentiality-only impact.
Likely exposure
Exposure is limited to the Microsoft Windows 10 and Windows Server versions listed in the source bundle: Version 2004 and 20H2 families. Systems already updated according to Microsoft guidance are likely lower risk.
Exploitation context
The source bundle does not show CISA KEV listing or cited active exploitation. CVSS marks exploit maturity as unproven. Required user interaction materially reduces urgency compared with wormable SMB issues.
Researcher notes
Evidence is sparse beyond Microsoft and CVE metadata. The bundle identifies a security feature bypass in the SMB client but does not describe the bypassed control, attack scenario, or compensating configuration mitigations.
Mitigation direction
- Apply Microsoft guidance for CVE-2021-31205 through normal Windows security updates.
- Prioritize unpatched Windows 10 and Windows Server 2004/20H2 assets.
- Confirm SMB client exposure assumptions with endpoint and server inventory.
- Monitor Microsoft advisory updates for any changed remediation guidance or exploitation notes.
Validation and detection
- Inventory Windows 10 and Windows Server 2004/20H2 systems.
- Check whether applicable Microsoft security updates for CVE-2021-31205 are installed.
- Verify vulnerability scanners map findings to the affected products in the source bundle.
- Review exposure of systems that initiate SMB connections to untrusted networks.
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-2021-31205 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
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C2.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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-2021-31205CVE 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.