CVE-2026-83989
Summary
by MITRE • 09/08/2026
Out-of-bounds read in Windows Services for NFS ONCRPC XDR Driver allows an unauthorized attacker to deny service over a network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified as an out-of-bounds read within the Windows Services for Network File System (NFS) component specifically targets the ONC/RPC Extensible Data Representation mechanism, commonly known as XDR. This flaw resides in the driver responsible for parsing and processing incoming network packets that utilize this protocol standard. The underlying technical defect occurs when the system fails to adequately validate the length of data fields contained within an RPC request before attempting to read from them. Consequently, if a crafted packet contains malformed or maliciously constructed headers indicating a larger payload size than what is actually present in the buffer, the driver will attempt to access memory addresses beyond the allocated boundaries. This behavior constitutes a classic out-of-bounds read condition, where the application reads data that it does not own, potentially exposing sensitive information from adjacent memory regions or causing an immediate crash of the processing thread due to invalid memory access violations.
From an operational perspective, this vulnerability poses a significant risk to service availability and system stability. Because the flaw is triggered by network traffic directed at the NFS services, it can be exploited remotely without requiring prior authentication on many default configurations. An unauthorized attacker positioned within reach of the vulnerable host can send specially crafted packets that induce the out-of-bounds read condition. The most immediate impact observed in such scenarios is a denial of service, as the resulting memory access violation typically causes the affected system process or even the entire operating system to halt unexpectedly. This leads to unplanned downtime and disrupts any dependent network file sharing operations, effectively rendering the NFS infrastructure unavailable until the system is manually restarted or patched.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-125, which describes out-of-bounds read vulnerabilities where a program reads data past the end of a buffer. In terms of offensive security frameworks, this exploit vector corresponds to MITRE ATT&CK technique T1498.002, specifically Network Denial of Service via resource exhaustion or system crashes triggered by malformed input. The attack relies on the principle that improper validation of external inputs allows an adversary to manipulate program flow and cause instability. It is important to note that while out-of-bounds reads can sometimes lead to information disclosure if the attacker can interpret the leaked memory contents, in this specific context involving kernel-mode drivers or critical system services, the primary consequence remains service disruption due to crash conditions rather than data exfiltration.
Mitigation strategies for this vulnerability primarily involve applying the latest security updates provided by Microsoft that address the input validation logic within the ONC/RPC XDR driver. Administrators should ensure that all systems running Windows Services for NFS are fully patched with the relevant cumulative update or standalone fix released to resolve this specific issue. Furthermore, given the remote network-based nature of the attack, it is advisable to restrict access to NFS services through firewall rules and network segmentation policies. By limiting which IP addresses can communicate with the NFS service on port 111 (RPC) and associated data ports, organizations can significantly reduce the attack surface. Additionally, disabling Windows Services for NFS if they are not actively required by business operations eliminates the vulnerability entirely by removing the vulnerable code path from the system environment.