SYSTEM privilege escalation via reentrant ResetDC callback
Published Oct 13, 2021 · Updated Oct 21, 2025
Use-after-free in Microsoft Windows Win32k allows local users to gain SYSTEM privileges through a crafted ResetDC callback. GreResetDCInternal retains PDC and PDEV references across an hdcOpenDCW user-mode callback, where a nested ResetDC call frees the original device context before those references are reused. Code must already run at medium integrity; successful exploitation enables controlled kernel memory access and execution as SYSTEM.
Summary
What happened
Use-after-free in Microsoft Windows Win32k allows local users to gain SYSTEM privileges through a crafted ResetDC callback. GreResetDCInternal retains PDC and PDEV references across an hdcOpenDCW user-mode callback, where a nested ResetDC call frees the original device context before those references are reused. Code must already run at medium integrity; successful exploitation enables controlled kernel memory access and execution as SYSTEM.
The record
- CVE
- CVE-2021-40449
- Published
- Oct 13, 2021
- Updated
- Oct 21, 2025
- Vendor
- Microsoft
- Product
- Windows 10 Version 1507
- Classifications
- CWE-416, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Oct 13, 2021CVE publishedPublication date reported by the CVE source.
- Nov 17, 2021Exploitation reportedCISA Known Exploited Vulnerabilities entry
- Oct 21, 2025Record 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 <10.0.10240.19086
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.
Public exploit references
- KaLendsi CVE-2021-40449 exploitproof of concept · demonstrated
- CallbackHellfunctional · demonstrated
- Win32k NtGdiResetDC Metasploit moduleweaponized · validated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Reported exploitation
- Ransomware-associated exploitationransomware
- CISA Known Exploited Vulnerabilities entryknown exploited catalog
- IronHusky-linked activitythreat actor
- MysterySnail exploitation campaignreported exploitation
Technologies
Your stack
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Your stack
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