Security readout for executives and security teams
Plain-English summary
CVE-2021-31957 is a Microsoft ASP.NET Core denial-of-service issue. A successful attack could make an affected application or service unavailable, but the public data rates exploitation complexity as high and shows no confidentiality or integrity impact.
Executive priority
Schedule remediation through normal vulnerability management, with faster handling for public-facing ASP.NET Core services. The issue is availability-focused and medium severity, but service downtime can still create business impact.
Technical view
The CVSS 3.1 vector is AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H, scoring 5.9. The source bundle lists affected Microsoft .NET Core 3.1, .NET 5.0, and several Visual Studio 2019 release lines. Specific vulnerable request conditions are not described in the provided sources.
Likely exposure
Exposure is most likely where ASP.NET Core applications run on affected .NET Core 3.1 or .NET 5.0 runtimes, or where listed Visual Studio 2019 builds are present in development or build environments.
Exploitation context
The bundle does not identify active exploitation, and KEV status is false. The CVSS vector indicates remote unauthenticated reachability, but high attack complexity. Treat internet-facing ASP.NET Core services as the main operational concern.
Researcher notes
The public bundle is sparse: it confirms affected product families, CVSS, advisory sources, and official remediation availability, but does not describe root cause, triggering conditions, or proof-of-concept status. Avoid assuming exploitability beyond the CVSS and vendor advisories.
Mitigation direction
- Review Microsoft MSRC guidance for exact fixed builds.
- Apply Microsoft updates for affected .NET and Visual Studio versions.
- Apply relevant Fedora package updates where Fedora packages are used.
- Prioritize internet-facing ASP.NET Core services first.
- Document any exception where fixed builds cannot be deployed.
Validation and detection
- Inventory deployed .NET Core 3.1 and .NET 5.0 runtimes.
- Identify Visual Studio 2019 versions listed in the advisory.
- Confirm production ASP.NET Core hosts run fixed vendor builds.
- Check Fedora systems for the referenced package advisories.
- Verify monitoring covers availability degradation after remediation.
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-2021-31957 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
- 5.9 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/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:H/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C2.23.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.9MediumVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H/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-2021-31957CVE reference · x_refsource_MISC
- FEDORA-2021-4b3fc547feCVE reference · vendor-advisory, x_refsource_FEDORA
- FEDORA-2021-cb4f3ab817CVE reference · vendor-advisory, x_refsource_FEDORA
- FEDORA-2021-1e0e04958dCVE reference · vendor-advisory, x_refsource_FEDORA
- FEDORA-2021-e9c84e6d26CVE reference · vendor-advisory, x_refsource_FEDORA
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.