When a client makes a request to use a file system and subsequently makes that file system available as a local resource, the client is said to "mount" the file system. The vulnerability lies in the software on the NFS server that handles requests to mount file systems. This software is usually called "mountd", "rpc.mountd, or nfsd."
Intruders who exploit the vulnerability are able to gain administrative access to the vulnerable NFS file server. That is, they can do anything the system administrator can do. This vulnerability can be exploited remotely and does not require an account on the target machine.
On some vulnerable systems, the mountd software is installed and enabled by default.
We have received reports indicating that intruders are actively using this vulnerability to compromise systems and are engaging in large-scale scans to locate vulnerable systems.
On some systems, the vulnerable NFS server is enabled by default.
Consider disabling NFS until you are able to install the patch. In particular, since some systems have vulnerable versions of mountd installed and enabled by default, we recommend you disable mountd on those systems unless you are actively using those systems as NFS servers.