EUVD-2026-56655
GHSA-fgq2-7g5m-ch5h
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local kernel driver heap overflow requiring only a standard user account; no interaction needed; full C/I/A impact via SYSTEM privilege gain.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Heap-based buffer overflow in Windows Cloud Files Mini Filter Driver allows an authorized attacker to elevate privileges locally.
AnalysisAI
Heap-based buffer overflow in the Windows Cloud Files Mini Filter Driver (CldFlt.sys) enables a low-privileged local attacker to escalate to SYSTEM-level privileges across a broad range of Windows 10, Windows 11, and Windows Server releases. The CVSS vector (AV:L/AC:L/PR:L/UI:N) confirms exploitation requires only a standard user account with no user interaction and no special configuration - a reliable post-access escalation primitive. Microsoft has released patches; no public exploit code or CISA KEV listing is present in the provided data.
Technical ContextAI
The Windows Cloud Files Mini Filter Driver (CldFlt.sys) is a kernel-mode filter driver implementing the Cloud Files API (cfapi.h), which underpins cloud storage virtualization features such as OneDrive on-demand sync. Filter drivers operate in ring-0 and process I/O request packets (IRPs) between the filesystem and user applications. CWE-122 (Heap-based Buffer Overflow) indicates the driver writes beyond the bounds of a heap-allocated buffer, enabling an attacker to corrupt adjacent kernel heap metadata or objects. In kernel context, controlled heap corruption can be leveraged to overwrite security-sensitive structures (e.g., token objects, function pointers) to redirect execution and gain SYSTEM privileges. The attack surface exists wherever CldFlt.sys is loaded, which is the default on all modern Windows editions that ship with cloud storage integration.
RemediationAI
Apply the vendor-released security update from Microsoft via Windows Update or WSUS immediately; the patch brings affected builds to the fixed versions listed above (e.g., Windows 10 22H2 to 10.0.19045.7663, Windows 11 24H2 to 10.0.26100.9168, Windows Server 2025 to 10.0.26100.33296 - see the full list in Affected Products). The advisory is at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-62771. If patching is temporarily blocked (e.g., change-freeze windows), a partial compensating control is to restrict interactive or remote-desktop login to only trusted, fully-vetted user accounts on high-value systems, reducing the pool of potential attackers who can reach the local execution context - however, this does not eliminate the vulnerability if any local user account is compromised. Disabling the Cloud Files Mini Filter Driver (CldFlt.sys) is theoretically possible via Group Policy but would break OneDrive on-demand sync and any ISV cloud storage provider using the Cloud Files API, making it impractical in most enterprise environments. Prioritize patching over workarounds.
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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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