CVE-2026-69955 in Windows
Summary
by MITRE • 10/14/2026
Out-of-bounds read in Windows Client for NFS allows an unauthorized attacker to disclose information over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified as an out-of-bounds read within the Microsoft Windows Client for Network File System represents a critical memory safety flaw that compromises the integrity and confidentiality of data processed by the operating system's file sharing subsystems. This specific component, which enables Windows machines to access files stored on remote NFS servers, contains logic errors in how it handles incoming network packets or parsed file attributes. When an attacker crafts maliciously formatted requests designed to exploit this parsing routine, they can trigger a memory read operation that accesses buffer regions beyond the allocated boundaries of the intended data structure. This type of flaw is classically categorized under CWE-125, which defines out-of-bounds read vulnerabilities where software reads data past the end or before the beginning of the intended buffer. The existence of this vulnerability allows an unauthorized attacker to leverage network-based interactions with the vulnerable service to extract sensitive information from the kernel memory space or user-mode application buffers that should remain isolated and protected.
From a technical perspective, the exploitation mechanism relies on the precise manipulation of input data sent over the NFS protocol. By sending specially crafted packets containing malformed headers or attribute lists, an attacker can cause the Windows Client for NFS to misinterpret buffer lengths or offsets. This miscalculation leads the application to read memory locations that are not part of the legitimate response payload. The information disclosed through this out-of-bounds access may include stack contents, heap metadata, or other sensitive data residing in adjacent memory regions. Such disclosures can provide attackers with valuable intelligence about the system's internal state, potentially facilitating further exploitation steps such as bypassing security mitigations like Address Space Layout Randomization (ASLR) or identifying specific software versions and configurations running on the target machine. This aligns with ATT&CK technique T1082, which involves System Information Discovery, where adversaries gather detailed information about the victim's environment to plan subsequent attacks.
The operational impact of this vulnerability is significant due to its potential for remote code execution or severe data leakage without requiring user interaction if the service is exposed and accessible over a network. Although classified primarily as an information disclosure issue in initial reports, out-of-bounds reads are often precursors to more dangerous exploits because they allow attackers to leak pointers that can be used to achieve arbitrary read/write primitives. In enterprise environments where NFS clients are commonly deployed for interoperability with Unix or Linux file servers, this vulnerability presents a wide attack surface. An attacker positioned on the same network segment could probe multiple systems simultaneously, exploiting the flaw to gather credentials, encryption keys, or other secrets stored in memory. The lack of authentication requirements for some NFS operations exacerbates the risk, allowing unauthenticated attackers to trigger the condition remotely over TCP/IP networks.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. Microsoft has addressed this issue through security updates that patch the underlying parsing logic within the Windows Client for NFS component. Organizations should prioritize applying these patches across all systems running affected versions of Windows, particularly those configured as NFS clients with network exposure. In addition to patching, defensive measures include restricting access to NFS services using firewall rules and Access Control Lists (ACLs) to limit connectivity only to trusted IP addresses. Network segmentation can further reduce the risk by isolating file server traffic from general-purpose networks. Furthermore, enabling advanced logging for NFS operations allows security teams to monitor for anomalous packet patterns that might indicate exploitation attempts. Regular vulnerability assessments and penetration testing should be conducted to identify any residual exposure or misconfigurations in network file sharing services. Adhering to the principle of least privilege ensures that only necessary protocols are enabled and exposed, thereby reducing the overall attack surface available to potential adversaries seeking to exploit memory corruption vulnerabilities like this one.