SB2026021096 - Multiple vulnerabilities in Microsoft Windows Subsystem for Linux

Description

This security bulletin contains information about 2 vulnerabilities.

1) Use-after-free (CVE-ID: CVE-2026-21242)

CWE-ID: CWE-416 - Use After 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 compromise vulnerable system.

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

2) Race condition (CVE-ID: CVE-2026-21237)

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 Subsystem for Linux. A local user can exploit the race and gain unauthorized access to sensitive information and escalate privileges on the system.

Remediation

Install update from vendor's website.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21242
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21237