Patch tracker / CVE reference / CVE-2026-21218

CVE-2026-21218

CVE-2026-21218 is a high severity Microsoft vulnerability with a CVSS score of 7.5. Microsoft has shipped the fix: deploy one of the 3 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

1.0%

EPSS, 30 days

High

Severity

Not in the CISA KEV catalog. EPSS exploit probability 1.0%. CVSS 7.5 (High).

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

Senserva AI Opinion for CVE-2026-21218

A spoofing flaw in .NET affecting the 10.0 runtime on macOS and Windows plus .NET 8.0 on Linux, rated High Severity at CVSS 7.5. With an exploit probability of just 1 percent and no known exploitation, this is among the lowest-urgency items in the current batch. The practical risk is applications built on these runtimes accepting content whose origin claims cannot be trusted.

Do this: Roll this into your standing monthly .NET runtime update across Windows, Linux, and macOS hosts.

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

Senserva AI Opinion and rich prompt for CVE-2026-21218

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-2026-21218 (source: https://senserva.com/cve/CVE-2026-21218.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2026-21218: High severity Microsoft vulnerability, CVSS 7.5
- EPSS 30-day exploitation probability: 1.0%
- Actively exploited (CISA KEV): no
- Fixed by: KB5077862, KB5077863, KB5077864
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 1%.

Fixed by KB5077862 and 2 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-2026-21218

Moderate priority: schedule it in your normal patch cycle. In Intune or Defender, confirm whether the fixing updates KB5077862, KB5077863, KB5077864 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-2026-21218. 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.

KB5077862 KB5077863 KB5077864

Scope and sources

Affected products

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.