#VU57249 Use-after-free in Windows and Windows Server - CVE-2021-40449

Vulnerability identifier: #VU57249

Vulnerability risk: High

CVSSv4.0: 8.5 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:A/U:Amber]

CVE-ID: CVE-2021-40449

CWE-ID: CWE-416

Exploitation vector: Local

Exploit availability: Yes

Vulnerable software:
Windows
Operating systems & Components / Operating system
Windows Server
Operating systems & Components / Operating system

Vendor: Microsoft

Description
The vulnerability allows a local user to escalate privileges on the system.

The vulnerability exists due to a boundary error within the Win32k NtGdiResetDC function in Microsoft Windows kernel. A local user can run a specially crafted program to trigger a use-after-free error, when the function ResetDC is executed a second time for the same handle during execution of its own callback, and execute arbitrary code with elevated privileges.

Note, the vulnerability is being actively exploited in the wild.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Windows: 7, 8.1 RT - 8.1, 10 Gold, 10 S, 10 Mobile, 10 20H2 10.0.19042.572, 10 21H1 10.0.19043.985, 10 1507 10.0.10240.16405, 10 1511 10.0.10586.3, 10 1607 10.0.14393.10, 10 1703 10.0.15063.138, 10 1709 10.0.16299.19, 10 1803 10.0.17134.48, 10 1809 10.0.17763.1, 10 1903 10.0.18362.116, 10 1909 10.0.18363.476, 10 2004 10.0.19041.264, 10, 11 21H2 10.0.22000.194

Windows Server: 2008 R2 - 2008, 2012 R2 - 2012, 2016 10.0.14393.10, 2019 10.0.17763.1 - 2019 2004

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External links
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-40449
https://securelist.com/mysterysnail-attacks-with-windows-zero-day/104509/
https://www.virustotal.com/gui/file/b7fb3623e31fb36fc3d3a4d99829e42910cad4da4fa7429a2d99a838e004366e

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Q & A

Can this vulnerability be exploited remotely?

No. This vulnerability can be exploited locally. The attacker should have authentication credentials and successfully authenticate on the system.

Is there known malware, which exploits this vulnerability?

Yes. This vulnerability is being exploited in the wild.