Double free in Microsoft Windows and Windows Server - CVE-2026-21530

Vulnerability identifier: #VU131207

CSH Severity: Medium

CVSS v4: 5.4 [CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-21530

CWE-ID: CWE-415

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to escalate privileges on the system.

The vulnerability exists due to a boundary error in Windows Rich Text Edit. A remote user can trick a victim to open a specially crafted file, win a race condition and gain elevated elevated privileges on the target system.

Microsoft Windows
Windows Server

Install updates from vendor's website.

Microsoft Windows - addressed in versions 10 21H2 10.0.19044.7291, 10 22H2 10.0.19045.7291, 10 1607 10.0.14393.9140, 10 1809 10.0.17763.8755, 11 23H2 10.0.22631.7079, 11 24H2 10.0.26100.8390, 11 24H2 10.0.26100.8457, 11 25H2 10.0.26200.8457, 11 26H1 10.0.28000.2113
Windows Server - addressed in versions 2012 R2 6.3.9600.23181, 2012 6.2.9200.26079, 2016 10.0.14393.9140, 2019 10.0.17763.8755, 2022 23H2 10.0.25398.2330, 2022 10.0.20348.5139, 2025 10.0.26100.32860

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21530

• Multiple vulnerabilities in Microsoft Windows Rich Text Edit