SB2026021054 - Multiple vulnerabilities in Microsoft Windows Kernel

Description

This security bulletin contains information about 4 vulnerabilities.

1) Heap-based buffer overflow (CVE-ID: CVE-2026-21245)

CWE-ID: CWE-122 - Heap-based Buffer Overflow

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 boundary error in Windows Kernel. A local user can pass specially crafted data to the application, trigger a heap-based buffer overflow and gain elevated privileges on the target system.

2) Inclusion of Sensitive Information in Log Files (CVE-ID: CVE-2026-21222)

CWE-ID: CWE-532 - Information Exposure Through Log Files

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

The vulnerability allows a local user to gain access to sensitive information.

The vulnerability exists due to software stores sensitive information into log files in Windows Kernel. A local user can read the log files and gain access to sensitive data.

3) Race condition (CVE-ID: CVE-2026-21231)

CWE-ID: CWE-362 - Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

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 race condition in Windows Kernel. A local user can exploit the race and gain unauthorized access to sensitive information and escalate privileges on the system.

4) Heap-based buffer overflow (CVE-ID: CVE-2026-21239)

CWE-ID: CWE-122 - Heap-based Buffer Overflow

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 boundary error in Windows Kernel. A local user can pass specially crafted data to the application, trigger a heap-based buffer overflow and gain elevated privileges on the target system.

Remediation

Install update from vendor's website.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21245
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21222
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21231
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21239