CVE-2021-40450
Win32k Elevation of Privilege Vulnerability
- CVSS
- 7.8Highscored by the publisher (CNA)
- Exploited in the wild
- Yes, in CISA KEV since 25 Apr 2022CISA deadline for US federal agencies: 16 May 2022
- EPSS
- 1.5%chance of exploitation in the next 30 daystop 26% of scored CVEsFIRST score of 11 Nov 2026
- Fix
- Patch availablesee the advisories in the references
- Published
- 13 Oct 2021analysed here 12 Nov 2026
Do first. Apply updates per vendor instructions. (CISA's required action for this KEV entry)
Summary
Triage
- Exploitable
- At runtime
- Attack vector
- local
- Can a WAF block it?
- No. See why
The summary, impact and action text on this page are written by our AI analysis pipeline, or taken from the NVD description when a CVE was imported from NVD. They are not the vendor's wording: check them against the sources. A longer AI executive summary and technical analysis are generated for signed-in accounts on the Max plan.
Affected products
| Product | Affected versions | Vendor says fixed in |
|---|---|---|
| Microsoft Windows 10 Version 1809 | >= 10.0.0 and < 10.0.17763.2237Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 1909 | >= 10.0.0 and < 10.0.18363.1854Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 2004 | >= 10.0.0 and < 10.0.19041.1288Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 20H2 | >= 10.0.0 and < 10.0.19042.1288Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 21H1 | >= 10.0.0 and < 10.0.19043.1288Vendor says fixed in: not stated | |
| Microsoft Windows 11 version 21H2 | >= 10.0.0 and < 10.0.22000.258Vendor says fixed in: not stated | |
| Microsoft Windows Server 2019 | >= 10.0.0 and < 10.0.17763.2237Vendor says fixed in: not stated | |
| Microsoft Windows Server 2019 (Server Core installation) | >= 10.0.0 and < 10.0.17763.2237Vendor says fixed in: not stated | |
| Microsoft Windows Server 2022 | >= 10.0.0 and < 10.0.20348.288Vendor says fixed in: not stated | |
| Microsoft Windows Server version 2004 | >= 10.0.0 and < 10.0.19041.1288Vendor says fixed in: not stated | |
| Microsoft Windows Server version 20H2 | >= 10.0.0 and < 10.0.19042.1288Vendor says fixed in: not stated |
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.
Products named in our analysis
- microsoft:windows_10_1809
- microsoft:windows_10_1909
- microsoft:windows_10_2004
- microsoft:windows_10_20h2
- microsoft:windows_10_21h1
- microsoft:windows_11_21h2
- microsoft:windows_server_2004
- microsoft:windows_server_2019
- microsoft:windows_server_2022
- microsoft:windows_server_20h2
Fix and mitigation
WAF and other mitigations
Can a WAF block it? No. The attack needs local access to the machine, so a WAF is not on its path.
Also consider: patch
Based on the attack vector (local or physical access). We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Remediation steps (AI-written)
Step-by-step remediation is generated for accounts on the Max plan, for CVEs that match a technology in their stack. Add this technology to your stack to see the fix checklist.
Exploitation evidence
- CISA KEV catalog
- Listed since 25 Apr 2022.
- CISA due date
- 16 May 2022, the remediation deadline for US federal agencies
- CISA required action
- Apply updates per vendor instructions.
- Public exploit code
- None on record in Exploit-DB, Metasploit, Nuclei templates or PoC-in-GitHub.
- CISA SSVC
- exploitation active, automatable no, technical impact totalAssessed by CISA 4 Feb 2025 (SSVC 2.0.3). Exploitation is none, poc (public proof of concept) or active.
Timeline
- 13 Oct 2021Published
- 25 Apr 2022Added to CISA KEV (exploited in the wild)194 days (about 6 months) later
- 16 May 2022CISA remediation due date (US federal agencies)21 days later
- 4 Feb 2025CISA SSVC assessment: exploitation active996 days (about 3 years) later
- 21 Oct 2025CVE record last updated259 days (about 9 months) later
- 12 Nov 2026Analysed by vulneraibility.com387 days (about 1 year) later
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
| Metric | Value | What it means |
|---|---|---|
| Attack vector | LocalLocal access required (shell, logged-in user). | Local access required (shell, logged-in user). |
| Attack complexity | LowRepeatable attack, no special conditions. | Repeatable attack, no special conditions. |
| Privileges required | LowThe attacker needs basic user privileges. | The attacker needs basic user privileges. |
| User interaction | NoneNo victim action needed. | No victim action needed. |
| Scope | UnchangedImpact stays within the vulnerable component. | Impact stays within the vulnerable component. |
| Confidentiality | HighTotal data disclosure possible. | Total data disclosure possible. |
| Integrity | HighComplete modification possible. | Complete modification possible. |
| Availability | HighFull outage possible. | Full outage possible. |
Common questions
Is CVE-2021-40450 being exploited?
Yes. CVE-2021-40450 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.
How severe is CVE-2021-40450?
CVE-2021-40450 is rated High with a CVSS score of 7.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2021-40450?
Yes. A fix has been recorded for CVE-2021-40450. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2021-40450 affect?
CVE-2021-40450 affects microsoft:windows_10_1809, microsoft:windows_10_1909, microsoft:windows_10_2004, microsoft:windows_10_20h2, and 6 further products or versions. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
References
2 references in the CVE record, grouped by the tags the record gives them.
Other links (2)
- portal.msrc.microsoft.com /en-US/security-guidance/advisory/CVE-2021-40450
- cisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-40450
Where the data on this page comes from
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA KEV catalog: exploitation, date added, due date
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.
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