Security readout for executives and security teams
Plain-English summary
A flaw in Microsoft Excel can let an attacker run code after a user interacts with malicious content. Successful exploitation could compromise data, alter systems, or interrupt operations. The issue affects multiple Microsoft 365, Excel, Office LTSC, Mac, and Office Online Server products listed by Microsoft.
Executive priority
Treat this as a high-priority patching issue because exploitation could enable code execution with severe business impact. Accelerate remediation on systems exposed to emailed, downloaded, or third-party spreadsheets, while avoiding claims of an active campaign without supporting evidence.
Technical view
CVE-2026-55948 is a use-after-free vulnerability, classified as CWE-416. Its CVSS 3.1 score is 7.8: local attack vector, low complexity, no privileges required, and user interaction required. Successful exploitation can cause high confidentiality, integrity, and availability impact.
Likely exposure
Exposure exists where listed Microsoft Excel, Microsoft 365 Apps, Office 2019, Office LTSC, Mac Office, or Office Online Server versions remain affected. Prioritize endpoints processing externally supplied or untrusted spreadsheet content. The bundle does not identify specific vulnerable configurations beyond the listed products and versions.
Exploitation context
The supplied sources do not establish active exploitation, and this CVE is not listed as KEV in the bundle. The CVSS vector marks exploit maturity as unproven. Exploitation requires user interaction and uses a local attack vector, but no further delivery conditions or indicators are provided.
Researcher notes
The weakness is memory-safety related: a use-after-free in Excel. CVSS reports low attack complexity, no required privileges, required user interaction, unchanged scope, and high impact across all three security objectives. The public bundle supplies no proof-of-concept details, root-cause depth, indicators, or confirmed exploitation evidence.
Mitigation direction
- Apply the Microsoft security update referenced by the MSRC advisory.
- Prioritize affected systems that routinely process untrusted spreadsheet files.
- Use existing controls to restrict or isolate untrusted Office content pending updates.
- Check Microsoft guidance for any product-specific remediation or deployment requirements.
Validation and detection
- Inventory installed versions of every listed Microsoft Office and Excel product.
- Compare installed builds with Microsoft’s affected and corrected version guidance.
- Confirm security updates installed successfully across managed endpoints and servers.
- Verify update coverage for Mac and Office Online Server deployments separately.
- Review available security telemetry; the supplied sources provide no indicators of compromise.
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-2026-55948 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.