Security readout for executives and security teams
Plain-English summary
This high-severity Microsoft Office vulnerability could let an unauthorized attacker run code with the affected user’s privileges. Successful exploitation could compromise sensitive information, alter files, or disrupt workstations. The supplied evidence describes local exploitation without required privileges or user interaction, but does not establish how an attacker reaches the vulnerable condition.
Executive priority
Treat this as a high-priority workstation patching issue. Identify affected Office deployments promptly and follow Microsoft’s remediation guidance. Accelerate coverage for privileged users and sensitive-data environments. Emergency incident response is not justified solely by the supplied evidence because active exploitation has not been established.
Technical view
CVE-2026-40358 is reported as a heap-based buffer overflow affecting multiple Microsoft Office editions on Windows and macOS. CVSS 3.1 is 8.4: local access, low complexity, no privileges, no user interaction, unchanged scope, and high confidentiality, integrity, and availability impact. The assigned CWE-416 denotes use-after-free, creating a source-level classification inconsistency requiring vendor clarification.
Likely exposure
Potential exposure includes Microsoft 365 Apps for Enterprise, Office 2016, Office 2019, Office LTSC 2021 and 2024, plus Office LTSC for Mac 2021 and 2024. The supplied version identifiers are broad and may not map directly to deployed build numbers, so organizations should confirm affected builds through Microsoft’s advisory.
Exploitation context
The supplied CVSS vector indicates local attack access, low complexity, no privileges, and no user interaction. CISA KEV status is false, and the exploit-maturity metric is unproven. Therefore, the supplied evidence does not support claiming active exploitation or publicly proven exploitation. Initial access requirements and the precise vulnerable Office component are not described.
Researcher notes
The bundle contains a notable inconsistency: the description says heap-based buffer overflow, while CWE-416 identifies use-after-free. The CVSS vector is local and requires neither privileges nor interaction, but no attack path, vulnerable component, affected-build ranges, or patch identifiers are supplied. Researchers should rely on Microsoft’s record for those details and avoid inferring a document-delivery vector.
Mitigation direction
- Review Microsoft’s CVE advisory for affected build and security-update details.
- Apply the applicable Microsoft security updates through the organization’s normal patch process.
- Prioritize Office installations on systems handling sensitive data or used by privileged personnel.
- Use endpoint protections and least-privilege accounts while patch deployment is completed.
Validation and detection
- Inventory installed Office products, platforms, update channels, and exact build numbers.
- Compare deployed builds with Microsoft’s current affected and remediated version guidance.
- Confirm applicable security updates installed successfully on representative Windows and macOS systems.
- Monitor endpoint telemetry for unexpected processes or file changes associated with Office applications.
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-2026-40358 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
- 8.4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/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:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C2.55.9microsoftVulnerability scoring details
Base CVSS 3.1 score
8.4HighVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/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 Office 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.