Patch tracker / CVE reference / CVE-2026-21265
CVE-2026-21265
Updated July 21, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.
Critical severity Microsoft vulnerability, CVSS 9.8. Fixed by 10 Microsoft security updates.
All about CVE-2026-21265: the Senserva AI read, whether it is exploited, the official patches, its change history, and the questions admins ask.
CVE-2026-21265 is a critical severity Microsoft vulnerability with a CVSS score of 9.8. Its EPSS score puts the probability of exploitation in the next 30 days at 73%. Microsoft has shipped the fix: deploy one of the 10 updates below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.
Risk summary
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Senserva AI Opinion for CVE-2026-21265
This is a Secure Boot certificate expiration bypass affecting Windows 10 Version 1809 (32-bit and x64) and Windows Server 2019, and it targets the boot integrity chain rather than a running application. Anyone still on the 1809 branch or Server 2019 relying on Secure Boot to block tampered bootloaders is exposed, and with a 73 percent EPSS score and Critical severity at CVSS 9.8 the odds of exploitation being developed are high even though it is not yet in CISA KEV.
Do this: Patch the affected 1809 and Server 2019 systems now, then verify Secure Boot is still enforcing after the update and that the boot certificates were renewed.
AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for CVE-2026-21265
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for CVE-2026-21265
Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.
Exploitation and severity
Not in the CISA KEV catalog. EPSS exploit probability 73%. CVSS 9.8 (Critical).
This CVE is among the top 25% of tracked Microsoft CVEs by EPSS exploit probability.
Official patch(es) for CVE-2026-21265
High priority: EPSS puts the odds of near-term exploitation high. In Intune or Defender, confirm whether the fixing updates KB5073379, KB5073450, KB5073455, KB5073457, KB5073696, KB5073698, KB5073722, KB5073723, KB5073724, KB5074109 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-2026-21265. 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.
Affected products
Common questions about CVE-2026-21265
Is CVE-2026-21265 actively exploited?
It is not currently listed in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score puts the probability of exploitation in the next 30 days at 73%.
What patch fixes CVE-2026-21265?
Microsoft fixed CVE-2026-21265 in KB5073379, KB5073450, KB5073455, KB5073457, KB5073696, KB5073698, KB5073722, KB5073723, KB5073724, KB5074109. Download from the Microsoft Update Catalog, or let Intune, Windows Update, or WSUS deliver it.
Which products are affected by CVE-2026-21265?
Windows 10 Version 1809 for 32-bit Systems, Windows 10 Version 1809 for x64-based Systems, Windows 11 Version 25H2 for ARM64-based Systems, Windows 11 Version 25H2 for x64-based Systems, Windows Server 2019.
Can I ask my own AI about CVE-2026-21265?
Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2026-21265's key facts: severity, CVSS, EPSS exploit probability, CISA KEV status, and the fixing KB. Copy it into Claude, ChatGPT, or Copilot for a triage plan; the data is refreshed three times a day (5 AM, 12:30 PM, and 7 PM US Central).
Fixed by the same updates
If you are patching CVE-2026-21265, the same updates also fix these:
Authoritative references
Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.
