Security readout for executives and security teams
Plain-English summary
A flaw in supported Microsoft Excel editions can let an attacker bypass a security protection after a user interacts with malicious content. Successful exploitation could compromise information, alter data, or disrupt the affected system. The available sources do not describe the bypassed feature or attack mechanism.
Executive priority
Treat as a high-priority patching issue because successful exploitation may have broad system impact. Prioritize exposed user populations and complete deployment promptly, while recognizing that the supplied evidence does not establish active exploitation.
Technical view
CVE-2026-20949 is an improper access control vulnerability (CWE-284) in Microsoft Office Excel. Its CVSS 3.1 score is 7.8: local access, low complexity, no privileges, and user interaction required, with potentially high confidentiality, integrity, and availability impact.
Likely exposure
Exposure applies to the listed Microsoft 365 Apps for Enterprise and Office LTSC 2021/2024 editions, including specified Mac editions. Actual exposure depends on installed builds and whether users interact with attacker-controlled Excel content. The bundle lacks detailed affected build ranges.
Exploitation context
The attack is local and requires user interaction, but requires no prior privileges and is rated low complexity. CISA KEV inclusion is not reported, and the supplied sources provide no evidence of active exploitation or public exploit availability.
Researcher notes
Public details are limited to improper access control and security-feature bypass classifications. The bypassed control, vulnerable component, triggering content, and build-specific ranges are not supplied. Avoid assuming a specific Excel protection or exploitation technique; use Microsoft’s advisory for current build and update details.
Mitigation direction
- Review the Microsoft advisory and deploy the applicable security update promptly.
- Inventory affected Microsoft 365 and Office LTSC installations, including Mac editions.
- Prioritize systems whose users regularly receive or open externally supplied spreadsheets.
- Follow any additional Microsoft mitigations if patching cannot occur immediately.
Validation and detection
- Compare installed Office products and builds with the current Microsoft advisory.
- Confirm the applicable Microsoft security update is installed successfully.
- Re-scan managed endpoints to identify missing or failed updates.
- Verify update coverage for both Windows and Mac Office deployments.
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-284: Authorization and privilege behavior lookup
Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. 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 lookupCVE-2026-20949 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 Security Feature Bypass 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.
Improper Access Control
Improper Access Control represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.