Security readout for executives and security teams
Plain-English summary
This high-severity Excel vulnerability could let an attacker run code after required user interaction. Successful exploitation could compromise data, alter systems, or disrupt operations with the user’s access. The source bundle identifies affected Microsoft 365, Excel, Office LTSC, Office 2019, Mac LTSC, and Office Online Server products.
Executive priority
Treat this as a high-priority patching issue because exploitation could produce full confidentiality, integrity, and availability impact. Prioritize user endpoints handling external documents and affected shared Office infrastructure. Escalate systems that cannot be updated promptly, but do not represent this CVE as actively exploited based on current evidence.
Technical view
An integer underflow or wraparound in Microsoft Office Excel, associated with CWE-191 and CWE-122, can result in local code execution. CVSS 3.1 rates it 7.8: local attack vector, low complexity, no privileges required, user interaction required, unchanged scope, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure exists where the listed Microsoft products and versions remain deployed. Risk is likely greatest on endpoints where users interact with attacker-influenced Excel content, although the bundle does not specify the exact delivery method, vulnerable components, fixed builds, or configuration prerequisites.
Exploitation context
The CVSS vector requires user interaction and describes a local attack vector; it does not support unauthenticated remote exploitation by itself. The bundle marks the CVE as absent from KEV and provides no evidence of active exploitation, public proof-of-concept availability, observed campaigns, or indicators of compromise.
Researcher notes
The available evidence identifies integer underflow and buffer-overflow weakness classes but omits the affected parser, triggering format, memory-corruption path, architecture-specific behavior, and fixed builds. Validate exposure against Microsoft’s advisory. Avoid assuming remote delivery, exploitation reliability, sandbox escape, privilege escalation, or active exploitation without additional cited evidence.
Mitigation direction
- Review Microsoft’s CVE advisory for applicable security updates and fixed build information.
- Prioritize updating affected Microsoft 365, Excel, Office LTSC, Office 2019, Mac, and Office Online Server deployments.
- Until updated, reduce user interaction with untrusted or unexpected Excel content.
- Use vendor-supported controls and guidance if immediate patching is operationally constrained.
Validation and detection
- Inventory the listed Microsoft products and deployed versions across endpoints and servers.
- Compare installed builds with the fixed-build information in Microsoft’s advisory.
- Confirm applicable updates installed successfully and devices completed any required restart.
- Re-scan managed assets to identify missed, offline, or failed-update systems.
- Document exceptions because the supplied sources provide no detection signatures or compromise indicators.
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-122: 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 lookupCWE-191: 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-2026-20957 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.
Heap-based Buffer Overflow
Heap-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Integer Underflow (Wrap or Wraparound)
Integer Underflow (Wrap or Wraparound) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.