Security readout for executives and security teams
Plain-English summary
This Microsoft Office Click-to-Run flaw can let a user who already has local, low-level access gain higher privileges. Successful exploitation could enable broad compromise of data, system integrity, and availability. It is serious for managed Windows endpoints, but the supplied evidence does not show remote exploitation or exploitation in the wild.
Executive priority
Treat this as a high-priority endpoint remediation issue, especially where users share systems or handle sensitive data. It is not described as remotely exploitable or actively exploited, so emergency isolation is not supported by the supplied evidence. Establish affected inventory, obtain exact fixed-build guidance from Microsoft, and verify update coverage promptly.
Technical view
CVE-2026-40418 is a CWE-416 use-after-free vulnerability in Microsoft Office Click-to-Run. CVSS 3.1 is 7.8: local access, low complexity, low privileges, no user interaction, unchanged scope, and high confidentiality, integrity, and availability impact. The source bundle identifies affected Office editions but does not provide fixed build numbers or deeper technical details.
Likely exposure
Potentially exposed systems are those running the listed versions of Microsoft 365 Apps for Enterprise, Office 2019, Office LTSC 2021, or Office LTSC 2024. Exposure requires an authorized attacker with local access. The bundle provides product-level versions but insufficient build detail to determine patch status from inventory alone.
Exploitation context
The vulnerability is locally exploitable by an authorized, low-privileged attacker and requires no user interaction. The bundle marks it as absent from KEV and supplies no evidence of active exploitation, public exploit availability, or a remote attack path. Local footholds from other incidents could increase its practical relevance.
Researcher notes
The bundle establishes a local CWE-416 elevation-of-privilege issue and a vendor patch reference, but omits the vulnerable component path, trigger conditions, fixed builds, and exploitability assessment beyond CVSS. The unusual product-version granularity should not be treated as sufficient for build-level detection. Avoid asserting active exploitation because no supporting source is supplied.
Mitigation direction
- Review Microsoft's CVE advisory for applicable security updates and exact fixed builds.
- Prioritize updating affected Office Click-to-Run installations on shared, privileged, or high-value endpoints.
- Restrict unnecessary local access and promptly remove inactive or excessive user accounts.
- Use endpoint controls to detect suspicious privilege changes while remediation is underway.
Validation and detection
- Inventory installed Office editions, versions, update channels, and Click-to-Run status.
- Compare deployed build numbers with Microsoft's current CVE advisory and update guidance.
- Confirm applicable Microsoft security updates installed successfully across managed endpoints.
- Review endpoint telemetry for unexpected privilege elevation involving Office Click-to-Run components.
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 lookupPrivilege behavior lookup
The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-40418 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:L/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:L/UI:N/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:L/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 Click-To-Run Elevation of Privilege 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.