Security readout for executives and security teams
Plain-English summary
This is a high-severity memory-safety flaw in Microsoft Excel. Successful exploitation could let an unauthorized attacker run code, potentially compromising data, applications, and system availability. User interaction is required, reducing—but not removing—the risk.
Executive priority
Treat as a high-priority patching issue because successful exploitation could fully affect confidentiality, integrity, and availability. Prioritize exposed users and services handling external spreadsheets, while recognizing that active exploitation is not established by the supplied evidence.
Technical view
CVE-2026-40359 is a use-after-free vulnerability (CWE-416) in Microsoft Office Excel. It carries CVSS 3.1 score 7.8 with local access, low complexity, no privileges, required user interaction, unchanged scope, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure exists where the listed Microsoft 365 Apps, Excel 2016, Office 2019, Office LTSC 2021/2024, Mac LTSC editions, or Office Online Server versions are deployed. The supplied data does not identify exact vulnerable build ranges or platform-specific update status.
Exploitation context
The supplied sources do not establish active exploitation, and this CVE is not listed as KEV in the bundle. Exploitation requires user interaction. No public exploit availability or attack campaign evidence is provided.
Researcher notes
The record identifies a use-after-free condition but provides no root-cause detail, vulnerable component, triggering format, exploit primitive, or precise fixed builds. The CVSS temporal metrics indicate unproven exploit maturity, an official fix, and confirmed report confidence. Consult the Microsoft advisory for build-level remediation details.
Mitigation direction
- Review Microsoft’s CVE advisory for product-specific security updates and deployment instructions.
- Prioritize updates for systems processing untrusted or externally supplied Excel content.
- Use existing controls to restrict untrusted Office files until affected systems are updated.
- Monitor Microsoft guidance for revised affected-build or mitigation information.
Validation and detection
- Inventory installations of every Microsoft product listed in the affected-product data.
- Compare installed builds against Microsoft’s current CVE update guidance.
- Confirm required security updates installed successfully across Windows, macOS, and server deployments.
- Review security telemetry for suspicious activity associated with Excel file handling.
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.
CWE-416: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution 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-2026-40359 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.
SSVC decision data
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:C1.85.9microsoftVulnerability 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
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- Microsoft Excel Remote Code Execution VulnerabilityCVE reference, microsoft · vendor-advisory, patch
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.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.