Executive brief
Windows Cloud Files Mini Filter Driver is a kernel component that enables cloud storage features like OneDrive Files On-Demand. A type confusion vulnerability allows a local authenticated attacker to achieve privilege escalation and potentially cause system crashes through malformed Cloud Filter API calls. This could lead to unauthorized access to sensitive files or system instability.
Technical details
The vulnerability is a type confusion flaw (CWE-843) in the CldiStreamPrepareRequestForMoreProcessing function of the Cloud Files Mini Filter Driver (cldflt.sys). The root cause involves a race condition where one thread walks an OpenStream request list while another thread inserts a stack-based sentinel, causing the abort walker to misinterpret the sentinel as a CLD_STREAM_REQUEST_PARTIAL object at offset +0x8. This results in the creation of a fake request object backed by kernel stack memory, which can be dereferenced and written through a forged pointer. An authenticated local attacker can trigger this by registering a provider, creating a dehydrated placeholder, initiating a read operation that creates a pending request, and then calling the CfAbortOperation API with wildcard values. Successful exploitation can lead to kernel arbitrary write primitives, privilege escalation, or denial of service; patches from Microsoft are available.
Affected products
- Microsoft Windows Cloud Files Mini Filter Driver 10.0.26100.8457, 10.0.26100.8655
Timeline
- 2026-09-08: disclosed
- 2026-09-26: other: Talos vulnerability report TALOS-2026-2445 published