Security readout for executives and security teams
Plain-English summary
CVE-2021-31939 is a high-severity Microsoft Excel remote code execution vulnerability. The source bundle indicates user interaction is required, so the business risk centers on users or services processing Office content with vulnerable Microsoft Office, Excel, Microsoft 365 Apps, Office Online Server, or Office Web Apps Server versions.
Executive priority
Treat as a high-priority patching issue for Office-heavy environments, especially where users or services handle untrusted spreadsheets or Office content. There is no sourced evidence of active exploitation here.
Technical view
The CVSS 3.1 vector is 7.8 high: AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. This means exploitation is local, low complexity, requires no privileges, requires user interaction, and can affect confidentiality, integrity, and availability. The bundle does not describe root cause or attack mechanics.
Likely exposure
Exposure is most likely where affected Microsoft Office, Excel, Microsoft 365 Apps for Enterprise, Office Online Server, or Office Web Apps Server 2013 SP1 versions remain unpatched or unmanaged.
Exploitation context
The bundle marks KEV as false and CVSS exploit maturity as unproven. No provided source states active exploitation. User interaction is required, but the bundle does not provide exploit details.
Researcher notes
The useful source-backed facts are CVSS, affected product families, official remediation availability, and lack of KEV listing. The bundle lacks root-cause, proof-of-concept, or exploit-chain detail, so deeper analysis requires vendor or advisory follow-up.
Mitigation direction
- Review Microsoft’s CVE-2021-31939 advisory for affected builds and updates.
- Apply Microsoft Office, Excel, and Office server security updates where applicable.
- Prioritize endpoints or servers handling external Office files.
- Use vendor guidance for any temporary mitigations or compensating controls.
Validation and detection
- Inventory installed Microsoft Office, Excel, Microsoft 365 Apps, and Office server versions.
- Compare installed builds against Microsoft’s advisory and Office security release guidance.
- Confirm update deployment succeeded on representative endpoints and servers.
- Check vulnerability management results for remaining CVE-2021-31939 detections.
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.
Execution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-31939 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
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C1.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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-2021-31939CVE reference · x_refsource_MISC
- https://www.zerodayinitiative.com/advisories/ZDI-21-670/CVE 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.