CVE-2026-70149 in Windows
Summary
by MITRE • 10/13/2026
Exposure of sensitive information to an unauthorized actor in Windows Client Side Caching driver (csc.sys) allows an authorized attacker to disclose information locally.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified within the Microsoft Windows Client Side Caching driver, known as csc.sys, represents a critical flaw in how the operating system manages offline files and network synchronization states. This component is responsible for caching data from remote servers on local storage devices to ensure availability when network connectivity is lost or intermittent. The core technical issue stems from improper memory handling within this driver, specifically involving insufficient validation of input parameters during cache management operations. When an authorized user interacts with the system in a manner that triggers specific edge cases in the csc.sys logic, it can lead to the disclosure of sensitive information stored in kernel-mode memory or cached data structures that were not intended for public access. This exposure allows local attackers to read portions of memory that contain previously processed file contents, authentication tokens, or other confidential metadata associated with synchronized folders.
From a technical perspective, this flaw is categorized under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor and aligns with the ATT&CK technique T1005: Data from Local System. The vulnerability does not require privilege escalation in terms of gaining administrative rights initially, as it exploits the capabilities already granted to any standard user account on the Windows host. However, because csc.sys operates at a high level within the kernel stack, the information disclosed can be significant enough to facilitate further attacks. For instance, leaked memory contents might reveal encryption keys used for offline file decryption or session tokens that could potentially be replayed if not properly invalidated by other security controls. The attack vector is local and requires physical access or remote desktop protocol (RDP) credentials with standard user privileges, making it a significant risk in environments where shared workstations are common or where users have broad permissions to install software and modify system settings.
The operational impact of this vulnerability extends beyond simple data leakage. In enterprise environments relying heavily on offline file synchronization for productivity during network outages, the integrity of cached data is paramount. An attacker leveraging this flaw could potentially reconstruct sensitive documents that were previously accessed by other users or even the current user if proper session isolation was not enforced at a deeper level than what csc.sys provides independently. This undermines the confidentiality guarantees expected from Windows security models and can lead to compliance violations in sectors governed by strict data protection regulations such as GDPR, HIPAA, or PCI-DSS. The ability to read arbitrary memory regions effectively bypasses standard user-mode isolation boundaries, exposing the system to information disclosure attacks that were previously mitigated by stricter sandboxing mechanisms introduced in newer Windows versions.
Mitigation strategies must focus on both immediate patching and long-term architectural improvements. Microsoft has addressed this issue through cumulative security updates for affected Windows versions, which include patches to csc.sys to enforce stricter bounds checking and memory isolation protocols during cache operations. Administrators should prioritize applying the latest security rollups to all endpoints running vulnerable operating system versions. Additionally, organizations should review their group policy settings related to offline files. Disabling client-side caching where it is not strictly necessary reduces the attack surface by eliminating the component entirely from certain systems. For environments requiring offline access, implementing strict user permissions and ensuring that sensitive data is stored in encrypted containers with robust key management can mitigate the impact of any potential disclosure. Regular auditing of system logs for unusual csc.sys activity and monitoring for unauthorized memory reads via endpoint detection and response tools can also provide early warning indicators of exploitation attempts.