Patch tracker / KB5002871

KB5002871: Office Online Server Security Update (May 2026)

KB5002871 is a High security update for Office Online Server, released 2026-05-12. It closes 3 CVEs with a maximum CVSS of 7.8. It is the 18th largest of the 61 updates Microsoft shipped that month, by CVEs closed.

Update summary

High
2026-05-12
Released
3
CVEs fixed
7.8
Max CVSS v3
High
Severity
Deploy this cycle
Fixes 3 CVEs for Office Online Server. No confirmed in-the-wild exploitation in this set today.

Fixes 3 CVEs. Most severe CVSS 7.8 (High). EPSS exploit probability up to <1%. Among the lower half of tracked Microsoft updates by EPSS exploit probability.

Senserva found thiswe track every release for this product line, so we can tell you this package is behind

A newer security update for Office Online Server has shipped since this one: KB5002884 (2026-08-11). For cumulative update families the newer package includes these fixes, so installing that one is usually the shorter path. Verify against your own update rings before you skip this package.

Senserva found thisno known issues as of our last check

We checked Microsoft's support article for KB5002871 on 2026-08-07 and it lists no known issues. Read the article before broad deployment; Microsoft adds issues as reports come in, and we re-check on every refresh.

Microsoft Update Catalog: download KB5002871Microsoft support article
Senserva AI Opinion for KB5002871

KB5002871 patches three CVEs across Office 2019 (both 32-bit and 64-bit) and Office Online Server, with the worst rated High severity at CVSS 7.8. Notably, Office Online Server is in scope here, so this is not purely a desktop client concern for organizations running that server role. Exploitation likelihood is currently low with 0 percent EPSS across all three CVEs and no CISA KEV or ransomware links.

Do this: Deploy KB5002871 to all Office 2019 installations and any Office Online Server hosts, prioritizing the server role since it is less likely to be covered by automatic client updates.

AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for KB5002871

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

Full tracking and change history for KB5002871

Released
2026-05-12
Last changed
2026-05-12
Changes tracked
1

Senserva began recording day-to-day change history on 2026-07-07, and refreshes it several times a day. Release dates are historical where Microsoft publishes them; revision history is tracked from that date forward, so it does not include changes made before then.

Check if KB5002871 is installed

Elevated PowerShell. No output means it is not installed.

CVEs fixed by this update

Sorted exploited-first, then by CVSS. Every CVE links to its Senserva page with the full risk facts, references, and a ready-to-paste AI prompt.

CVESeverityCVSSEPSSExploited
CVE-2026-40359High7.8<1%No
CVE-2026-40360High7.8<1%No
CVE-2026-40362High7.8<1%No

Scope and sources

Affected products
Also released in May 2026

KB5002863

9 CVEs · High · exploited

KB5002868

9 CVEs · High · exploited

KB5002870

9 CVEs · High · exploited

KB5094139

1 CVE · High · exploited

KB5094140

1 CVE · High · exploited

KB5094142

1 CVE · High · exploited

KB5094144

1 CVE · High · exploited

KB5078943

3 CVEs · Critical

The full month, summarized: Microsoft Patch Tuesday.

Authoritative references
Official KB5002871 page (Microsoft Support)Microsoft Update CatalogMicrosoft Security Update Guide

See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.

New to a term on this page? CVE, KB, KEV, CVSS, and EPSS are each explained once, on the Senserva security lexicon. Reference: Microsoft CVE and vulnerability management and the Microsoft patching guide.
Provided as is, without warranty; verify against the vendor advisory before acting. Data notice and terms.