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DETECTION OVERVIEW

Windows NFS ONCRPC Exploit Attempt - CVE-2021-26432

Risk Factors

Attackers must have read or write permission to any file on an NFS share on the targeted system. However, authentication is not required if the NFS share is configured with anonymous write access. If the exploit is successful, the attacker can cause a denial of service (DoS) or gain control of the Windows Server.

Kill Chain

Exploitation

Risk Score

61

Detection diagram
Next in Exploitation: Windows Print Spooler Exploit Attempt - CVE-2021-34527

Attack Background

The NFS protocol enables file transfers between devices with Windows and non-Windows operating systems. Part of NFS is the Open Network Computing Remote Procedure Call (ONCRPC) protocol, which enables remote access and data transfer between devices. Transferred data is encoded data with the External Data Representation (XDR) format. When NFS version 3 is installed on Windows systems, the XDR driver (rpcxdr.sys) has a vulnerability in how it processes security parameters in NFS requests. The exploitation of this vulnerability can cause an out-of-bounds write in the XDR driver, which can lead to a denial of service (DoS) or remote code execution (RCE).

Mitigation Options

Install relevant patches for affected versions

Disable anonymous write access to NFS shares unless require

MITRE ATT&CK ID

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