SYSTEM privilege escalation via stale WndExtra flag
Published Feb 25, 2021 · Updated Aug 12, 2026
Out-of-bounds write in Microsoft Windows Win32k allows local users to execute code with SYSTEM privileges via a crafted application. During xxxCreateWindowEx, a user-mode callback can change tagWND.WndExtra from a pointer to an offset, but the returned value overwrites it without clearing the offset flag. Low-privileged local execution is required; the stale flag drives unchecked kernel heap addressing, enabling arbitrary read and write operations and SYSTEM token replacement.
Summary
What happened
Out-of-bounds write in Microsoft Windows Win32k allows local users to execute code with SYSTEM privileges via a crafted application. During xxxCreateWindowEx, a user-mode callback can change tagWND.WndExtra from a pointer to an offset, but the returned value overwrites it without clearing the offset flag. Low-privileged local execution is required; the stale flag drives unchecked kernel heap addressing, enabling arbitrary read and write operations and SYSTEM token replacement.
The record
- CVE
- CVE-2021-1732
- Published
- Feb 25, 2021
- Updated
- Aug 12, 2026
- Vendor
- Microsoft
- Product
- Windows Server 2019
- Classifications
- CWE-269, CWE-787, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Feb 25, 2021CVE publishedPublication date reported by the CVE source.
- Aug 12, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=10.0.0 <publication
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- KaLendsi CVE-2021-1732 exploitfunctional · validated
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Reported exploitation
- Bitter APT targeted exploitationthreat actor
- CISA Known Exploited Vulnerabilities entryknown exploited catalog
Technologies
Your stack
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Your stack
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