EUVD-2026-56597
GHSA-mmrv-896m-g74r
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local attack vector and low-privilege requirement reflect standard user triggering the SYSTEM-running Installer service; full CIA impact reflects SYSTEM-level code execution with no scope change.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Heap-based buffer overflow in Windows Installer allows an authorized attacker to elevate privileges locally.
AnalysisAI
Privilege escalation in Windows Installer exposes all supported Windows systems to SYSTEM-level compromise by any low-privileged local user. The heap-based buffer overflow (CWE-122) in the Installer service requires only an authenticated local session - no user interaction, no elevated credentials, and low attack complexity per CVSS:3.1/AV:L/AC:L/PR:L/UI:N. No public exploit code or active exploitation via CISA KEV has been identified at time of analysis, but the ubiquity of Windows Installer and the straightforward exploitation conditions make this a meaningful post-compromise escalation primitive.
Technical ContextAI
Windows Installer (msiexec.exe and associated msi.dll) is the built-in Microsoft service responsible for installation, maintenance, and removal of software on Windows systems, running as the highly privileged SYSTEM account. CWE-122 (Heap-based Buffer Overflow) occurs when a program writes beyond the bounds of a heap-allocated memory buffer, corrupting adjacent heap metadata, function pointers, or object vtables. In the context of a privileged service such as Windows Installer, a successful overflow can redirect execution flow from within the SYSTEM process into attacker-controlled code, yielding full local privilege escalation. The CVSS vector confirms no special attack complexity or prerequisites beyond a valid low-privileged local account, consistent with a reachable code path triggered through standard installer invocation. No CPE strings were included in the provided intelligence data; specific affected Windows build numbers must be sourced from the MSRC advisory.
RemediationAI
Apply the Microsoft security update for CVE-2026-70345 via Windows Update, Windows Server Update Services (WSUS), or the Microsoft Update Catalog. The exact fixed KB number and patch version were not specified in the available intelligence data; refer to the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-70345 for the authoritative KB article. Where immediate patching is not feasible, restrict local interactive and remote desktop access to trusted personnel, reducing the pool of potential attackers who could trigger the vulnerable Windows Installer code path; note this does not eliminate risk but reduces exposure surface. Administrators may also configure Group Policy (Computer Configuration > Administrative Templates > Windows Components > Windows Installer > 'Disable Windows Installer') to restrict or disable Installer functionality, though this will prevent software installation workflows and should be weighed against operational impact. Enforce the principle of least privilege to ensure standard user accounts cannot be leveraged for lateral movement after privilege escalation.
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
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