Security readout for executives and security teams
Plain-English summary
This is a Microsoft Office remote code execution flaw affecting several Office, Excel, Microsoft 365 Apps, and Office web rendering products. A victim must interact with malicious content, but successful exploitation could allow code execution with serious confidentiality, integrity, and availability impact.
Executive priority
Prioritize normal high-severity patching, with faster action for exposed document-handling teams and Office server deployments. There is no supplied evidence of active exploitation, but the impact is full code execution if triggered.
Technical view
CVE-2021-31177 is rated CVSS 7.8 high with local attack vector, low complexity, no privileges required, and user interaction required. The supplied metadata lists Office 2019, Office 2019 for Mac, Microsoft 365 Apps for Enterprise, Excel 2013/2016, Office Online Server, and Office Web Apps Server as affected.
Likely exposure
Organizations using the listed Microsoft Office, Excel, Microsoft 365 Apps for Enterprise, Office Online Server, or Office Web Apps Server versions may be exposed, especially where users open untrusted Office documents.
Exploitation context
The supplied data does not show CISA KEV listing or confirmed active exploitation. CVSS exploit maturity is marked unproven. Treat this as a serious document-interaction risk, not as confirmed in-the-wild exploitation from the provided evidence.
Researcher notes
The source bundle does not include root-cause details, CWE classification, exploit method, or proof-of-concept evidence. Analysis should remain bounded to Microsoft’s advisory metadata, CVSS vector, affected product list, and ZDI reference.
Mitigation direction
- Apply Microsoft security updates for affected Office and Excel products.
- Patch Office Online Server and Office Web Apps Server where deployed.
- Prioritize users handling external or untrusted Office documents.
- Verify Microsoft guidance for product-specific update channels and supersedence.
- Maintain phishing and attachment controls to reduce malicious document exposure.
Validation and detection
- Inventory affected Microsoft Office, Excel, Microsoft 365 Apps, and server products.
- Confirm installed builds include Microsoft’s CVE-2021-31177 security update.
- Check whether Office Online Server or Office Web Apps Server is deployed.
- Review endpoint telemetry for suspicious Office child processes or crashes.
- Validate email and web controls inspect or block risky Office attachments.
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-2021-31177 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-2021-31177CVE reference · x_refsource_MISC
- https://www.zerodayinitiative.com/advisories/ZDI-21-576/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.