SB2026011373 - Multiple vulnerabilities in Microsoft Win32k

Description

This security bulletin contains information about 3 vulnerabilities.

1) Type Confusion (CVE-ID: CVE-2026-20811)

CWE-ID: CWE-843 - Type confusion

CVSSv4: 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:U/U:Clear

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

The vulnerability exists due to a type confusion error in Win32k. A local user can pass specially crafted data to the application, trigger a type confusion error and gain elevated privileges on the target system.

2) Double free (CVE-ID: CVE-2026-20863)

CWE-ID: CWE-415 - Double Free

CVSSv4: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear

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

The vulnerability exists due to a boundary error in Win32k. A local user can pass specially crafted data to the application, trigger double free error and gain elevated privileges on the target system.

3) Use-after-free (CVE-ID: CVE-2026-20920)

CWE-ID: CWE-416 - Use After Free

CVSSv4: 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:U/U:Clear

The vulnerability allows a local user to compromise vulnerable system.

The vulnerability exists due to a use-after-free error in Win32k. A local user can gain elevated privileges on the target system.

Remediation

Install update from vendor's website.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20811
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20863
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20920