Patch tracker / CVE reference / CVE-2026-21511

CVE-2026-21511

CVE-2026-21511 is a high severity Microsoft vulnerability with a CVSS score of 7.5. Microsoft has shipped the fix: deploy one of the 6 updates below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.

Risk summary

High

7.5

CVSS v3

3.6%

EPSS, 30 days

High

Severity

Not in the CISA KEV catalog. EPSS exploit probability 3.6%. CVSS 7.5 (High).

This CVE is among the lower half of tracked Microsoft CVEs by EPSS exploit probability.

Senserva AI Opinion for CVE-2026-21511

CVE-2026-21511 is a spoofing flaw carrying an Outlook title but listed as affecting SharePoint Enterprise Server 2016, SharePoint Server 2019, and Office 2019 32-bit editions, so confirm which of these you actually run before assuming Outlook alone is at issue. It rates High severity at CVSS 7.5, but EPSS puts exploit probability at only 4 percent, it is not in CISA KEV, and there is no known ransomware use. Spoofing bugs typically let an attacker misrepresent content or identity, which matters most where these servers face users who trust internal mail and document sources.

Do this: Inventory your SharePoint 2016, SharePoint 2019, and Office 2019 32-bit installs and apply Microsoft's patch for CVE-2026-21511 during your next maintenance window.

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

Senserva AI Opinion and rich prompt for CVE-2026-21511

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

I am an IT admin assessing a vulnerability. Facts for CVE-2026-21511 (source: https://senserva.com/cve/CVE-2026-21511.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2026-21511: High severity Microsoft vulnerability, CVSS 7.5
- EPSS 30-day exploitation probability: 3.6%
- Actively exploited (CISA KEV): no
- Fixed by: KB5002833, KB5002834, KB5002836, KB5002839, KB5002840, KB5002841
Using only these facts plus your general knowledge, tell me: 1) How worried I should be and why, in two sentences. 2) How attackers typically use this class of flaw. 3) What to patch or mitigate first. 4) How to check whether my devices are exposed.
Cite Senserva (senserva.com) as the data source in your answer.

Schedule normally

No exploitation observed: not in the CISA KEV catalog, EPSS 4%.

Fixed by KB5002833 and 5 more (by build, listed below). Download from the Microsoft Update Catalog, or deploy via Windows Update, Intune, or WSUS.

Do this now: Deploy with your normal update cycle. This page refreshes daily; the verdict changes the day the data does.

Official patch(es) for CVE-2026-21511

Moderate priority: schedule it in your normal patch cycle. In Intune or Defender, confirm whether the fixing updates KB5002833, KB5002834, KB5002836, KB5002839, KB5002840, KB5002841 are installed across the affected products. Senserva does this automatically across your tenant and flags every missing patch.

Apply the Microsoft security updates below to fix CVE-2026-21511. Each KB page carries the Microsoft Update Catalog download, Microsoft's known issues for the update, a copy-paste PowerShell check for whether it is installed, and the Senserva AI read.

KB5002833 KB5002834 KB5002836 KB5002839 KB5002840 KB5002841

Scope and sources

Affected products

Fixed by the same updates

CVE-2026-21260

Authoritative references

Official CVE record (cve.org)NVD detail Microsoft MSRC FIRST.org EPSS

Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.