EUVD-2026-56627
GHSA-c4qm-j6c8-f39x
Severity by source
AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Local-only trigger (AV:L), timing-dependent UAF race condition (AC:H), and low-privileged account prerequisite (PR:L) with full SYSTEM-level post-exploitation impact.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Use after free in Windows Installer allows an authorized attacker to elevate privileges locally.
AnalysisAI
Privilege escalation in Windows Installer (msiexec) on Windows 11 and Windows Server 2025 allows a locally authenticated low-privileged user to gain SYSTEM-level privileges by exploiting a use-after-free memory corruption condition. Affected builds span Windows 11 versions 24H2, 25H2, and 26H1, as well as Windows Server 2025 including Server Core deployments. No public exploit code or active exploitation has been identified at time of analysis; a vendor-released patch is available from Microsoft.
Technical ContextAI
Windows Installer is the built-in package management subsystem (msiexec.exe) present across all Windows editions, responsible for installing, modifying, and removing software. CWE-416 (Use After Free) occurs when a memory pointer continues to be dereferenced after the underlying heap object has been freed, enabling an attacker to reclaim that freed region with attacker-controlled data and redirect program control flow. In a privilege escalation context, the attacker manipulates the Installer's heap state during an installation or repair operation to corrupt internal structures and ultimately gain SYSTEM-level execution within the Installer process. CVSS vector metrics AV:L and AC:H indicate the flaw is triggered locally and requires a timing-dependent race condition, consistent with classic heap-UAF exploitation primitives. Affected version ranges are confirmed across CPE-equivalent build strings for Windows 11 (10.0.26100.x, 10.0.26200.x, 10.0.28000.x) and Windows Server 2025 (10.0.26100.x).
RemediationAI
Apply the Microsoft security update for CVE-2026-61938, targeting the following fixed builds: Windows 11 24H2 and Windows Server 2025 to build 10.0.26100.33296 or later, Windows 11 25H2 to build 10.0.26200.9168 or later, and Windows 11 26H1 to build 10.0.28000.2704 or later. Updates are distributed through Windows Update, Windows Server Update Services (WSUS), and the Microsoft Update Catalog; the full advisory with download links is at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-61938. Where immediate patching is not operationally feasible, restrict interactive and remote desktop logon rights to only explicitly trusted accounts to reduce the pool of principals capable of triggering the vulnerability (note: this does not eliminate the flaw and should be treated as a temporary measure only). Monitoring for anomalous msiexec.exe child process creation or unexpected SYSTEM-context processes can aid in detection of attempted exploitation.
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Same weakness CWE-416 – Use After Free
View allSame technique Denial Of Service
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External POC / Exploit Code
Leaving vuln.today