# CVE-2026-55121: Microsoft Office Information Disclosure Vulnerability

Status: published. Published: 2026-07-14. Updated: 2026-11-10.

Out-of-bounds read in Microsoft Office allows an unauthorized attacker to disclose information locally.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: microsoft) — https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55121

## Affected products and versions

- Microsoft / Microsoft 365 Apps for Enterprise: ≥ 16.0.1; < https://aka.ms/OfficeSecurityReleases (affected, custom). Source: CNA: microsoft; platforms: 32-bit Systems, x64-based Systems
- Microsoft / Microsoft Office 2016: ≥ 16.0.0; < 16.0.5561.1000 (affected, custom). Source: CNA: microsoft; platforms: 32-bit Systems, x64-based Systems
- Microsoft / Microsoft Office 2019: ≥ 19.0.0; < https://aka.ms/OfficeSecurityReleases (affected, custom). Source: CNA: microsoft; platforms: 32-bit Systems, x64-based Systems
- Microsoft / Microsoft Office 365 for Mac: ≥ 1.0.0; < 16.111.26071215 (affected, custom). Source: CNA: microsoft
- Microsoft / Microsoft Office LTSC 2021: ≥ 16.0.1; < https://aka.ms/OfficeSecurityReleases (affected, custom). Source: CNA: microsoft; platforms: 32-bit Systems, x64-based Systems
- Microsoft / Microsoft Office LTSC 2024: ≥ 16.0.0; < https://aka.ms/OfficeSecurityReleases (affected, custom). Source: CNA: microsoft; platforms: 32-bit Systems, x64-based Systems
- Microsoft / Microsoft Office LTSC for Mac 2021: ≥ 16.0.1; < 16.111.26071215 (affected, custom). Source: CNA: microsoft
- Microsoft / Microsoft Office LTSC for Mac 2024: ≥ 16.0.0; < 16.111.26071215 (affected, custom). Source: CNA: microsoft
- Microsoft / Microsoft SharePoint Enterprise Server 2016: ≥ 16.0.0; < 16.0.5561.1001 (affected, custom). Source: CNA: microsoft; platforms: x64-based Systems
- Microsoft / Microsoft SharePoint Server 2019: ≥ 16.0.0; < 16.0.10417.20175 (affected, custom). Source: CNA: microsoft; platforms: x64-based Systems
- Microsoft / Microsoft SharePoint Server Subscription Edition: ≥ 16.0.0; < 16.0.19725.20434 (affected, custom). Source: CNA: microsoft; platforms: x64-based Systems

## Severity and prioritization

- CVSS 3.1: 5.5 (medium); CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C; source: CNA: microsoft

- CISA KEV: No listing in collected sources

- EPSS: 0.51% as of 2026-11-10; percentile 44.05%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-125

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55121 (CNA: microsoft; vendor-advisory, patch)

## Provenance

- CNA: microsoft: https://www.cve.org/CVERecord?id=CVE-2026-55121; retrieved 2026-11-10; source updated 2026-11-10

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-55121; retrieved 2026-11-10; source updated Not reported

Revision: cf3e62426a056028fd82e50fbb5f593948dfd41ab407b2d26db71ab71e0ddd06

Canonical: https://y2.dev/cve/CVE-2026-55121

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

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