Windows Cloud Files CVE-2026-62771

Exploitation requires a local user session on the target Windows system - the attacker must be able to execute code as at least a standard (non-elevated) user (PR:L per CVSS vector). No user interaction is needed from any other account. The Cloud Files Mini Filter Driver (CldFlt.sys) must be loaded, which is the default state on all affected Windows editions listed above; no special feature enablement or non-default configuration is required beyond the driver being present. Exploitation is limited to local access only (AV:L) - remote unauthenticated exploitation is not possible. Scope is unchanged (S:U), meaning the attacker cannot pivot to other systems directly through this vulnerability alone; it is an escalation primitive, not a lateral movement vector.

The CVSS 7.8 score and its underlying vector (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) accurately reflect a high-severity local privilege escalation: low complexity, no user interaction, and full C/I/A impact. The attack requires only a foothold as a standard local user, making this a near-automatic escalation step in any post-exploitation chain. No EPSS data was provided, and no CISA KEV listing appears in the input - meaning confirmed in-the-wild exploitation is not established at time of analysis. However, LPE vulnerabilities in Windows kernel-mode drivers are consistently weaponized by ransomware operators and APT groups as second-stage tools after initial access, making the real-world risk high despite the absence of a KEV flag. No POC is referenced in the provided data, which reduces immediate spray-and-pray risk but does not lower the threat from targeted actors. The broad affected version range - spanning Windows 10 1809 through Windows 11 26H1 and all current Windows Server releases - amplifies organizational exposure. This should be treated as a priority patch given the prevalence of Windows, the low exploitation complexity, and the kernel-level impact.

An attacker who has obtained a standard local user session - through phishing, credential stuffing, or an earlier vulnerability - crafts a malformed I/O request targeting the vulnerable code path in CldFlt.sys, triggering the heap buffer overflow. The overflow corrupts an adjacent kernel heap object (such as a process token), allowing the attacker to impersonate SYSTEM and execute arbitrary code with full operating system privileges. No public proof-of-concept code is referenced in the available data, but the low attack complexity (AC:L) suggests the exploit primitive is straightforward once the overflow primitive is controlled.