Patch tracker / KB5002835
KB5002835: Office Online Server Security Update (February 2026)
KB5002835 is a High security update for Office Online Server, released 2026-02-10. It closes 3 CVEs with a maximum CVSS of 7.8. It is the 15th largest of the 31 updates Microsoft shipped that month, by CVEs closed.
Update summary
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.
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.
KB5002835 patches three CVEs (CVE-2026-21259, CVE-2026-21258, CVE-2026-21261) across Office Online Server and Office 2019 in both 32-bit and 64-bit editions, with a highest Severity of High at CVSS 7.8. The Office Online Server inclusion is the notable part here, since a shared server component means one host can expose many users rather than individual desktops alone. Neither of these CVEs is in the CISA KEV catalog or linked to ransomware, and the highest EPSS is only 1 percent, so this is patch-on-schedule rather than a drop-everything event.
Do this: Apply KB5002835 to your Office Online Server hosts first, then push it to Office 2019 32-bit and 64-bit desktops through your normal update ring.
AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for KB5002835
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5002835
- Released
- 2026-02-10
- Last changed
- 2026-02-10
- 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 KB5002835 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.
| CVE | Severity | CVSS | EPSS | Exploited |
|---|---|---|---|---|
| CVE-2026-21259 | High | 7.8 | <1% | No |
| CVE-2026-21258 | Medium | 5.5 | <1% | No |
| CVE-2026-21261 | Medium | 5.5 | <1% | No |
Scope and sources
- Affected products
- Also released in February 2026
KB5075897
29 CVEs · High · exploitedKB5075899
29 CVEs · High · exploitedKB5075904
24 CVEs · High · exploitedKB5075906
27 CVEs · High · exploitedKB5075912
24 CVEs · High · exploitedKB5075941
26 CVEs · High · exploitedKB5075942
29 CVEs · High · exploitedKB5075943
27 CVEs · High · exploitedThe full month, summarized: Microsoft Patch Tuesday.
- Authoritative references
See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.