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S-073: Vulnerability in SMBv2
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rexd(1M) rexd(1M) NAME
rexd - RPC-based remote execution server SYNOPSIS
log_file] mountdir] DESCRIPTION
is the RPC server for remote command execution. A is started by when a remote execution request is received (see inetd(1M)). exits when command execution has completed. If the user ID (uid) in the remote execution request is assigned to a user on the server, executes the command as that user. If no user on the server is assigned to the uid, does not execute the command. The option and security file allow for better access control (see inetd.sec(4)). For noninteractive commands, standard output and error file descriptors are connected to sockets. Interactive commands use pseudo termi- nals for standard input, output, and error (see pty(7)). If the file system specified in the remote execution request is not already mounted on the server, uses NFS to mount the file system for the duration of the command execution (see nfs(7)). mounts file systems with the and options. For more details on mount options see mount(1M). If the server cannot mount the file system, an error message is returned to the client. By default, any mount points required by are created below To change the default location, use the option. Options recognizes the following options and command-line arguments: Log any diagnostic, warning, and error messages to log_file. If log_file exists, appends messages to the file. If log_file does not exist, creates it. Messages are not logged if the option is not specified. Information logged to the file includes date and time of the error, host name, process ID and name of the function generating the error, and the error message. Note that different RPC services can share a single log file because enough information is included to uniquely identify each error. Create temporary mount points below directory mountdir. By default, creates temporary mount points below The directory mountdir should have read and execute per- mission for all users (mode 555). Otherwise, denies execution for users that do not have read and execute permis- sion. Use increased security checking. When started with the option, denies execution access to a client unless one of the following conditions is met: o The name of the client host is in file on the server. o The user on the server that is associated with the uid sent by the client has an entry in specifying the client name on a line or the client name followed by at least one blank and the user's name. For example, assume a user whose login name is is assigned to uid 7 on and executes the following command: User on must have one of the following entries in DIAGNOSTICS
The following is a subset of the messages that could appear in the log file if the option is used. Some of these messages are also returned to the client. was unable to the user's current working file system. See for more details. The path name mountdir, under which temporary mount points are created, is not a directory or does not exist. could not find command. was denied permission to execute command. The executable file is currently open for writing. was unable to execute command. does not allow execution as user The uid uid is not assigned to a user on the server. was started with the option and the remote execution request did not meet either of the conditions required by the option. The host host on which the user's current working directory is located is not running Therefore, is unable to mount the required file system (see mountd(1M)). The host on which the client's current working directory is located does not have the server on the export list for file system file_system containing the client's current working direc- tory. Therefore, is unable to mount the required file system. WARNINGS
The client's environment is simulated by but not completely recreated. The simulation of the client's environment consists of mounting the file system containing the client's current working directory (if it is not already mounted) and setting the user's environment variables on the server to be the same as the user's environment variables on the client. Therefore a command run by does not always have the same effect as a command run locally on the client. The protocol only identifies the client user by sending the uid of the client process and the host name of the client. Therefore, it is very difficult for to perform user authentication. If a user on the server is assigned to the uid sent by the client, executes the requested command as that user. If no user on the client is assigned to the uid sent by the client, returns an error. The option has been added to provide increased user authentication. However, the authentication provided is not foolproof, and is limited by the information passed by the protocol. In order to simulate the client's environment, mounts the file system containing the client's current working directory (if it is not already mounted). This mount is intended to be temporary for the duration of the command. If mounts a file system, it attempts to the file system after the command has completed executing. However, if receives a signal (see sig- nal(2)), the file system is not unmounted. The file system remains mounted until the superuser executes the appropriate command or the server is rebooted. attempt to umount the file system can also fail if the file system is busy. The file system is busy if it contains an open file or a user's current working directory. The file system remains mounted until the superuser executes the appropriate command or the server is rebooted. For more information on security issues, see Security issues and their consequences should be considered before configuring to run on a system. FILES
master pseudo terminals slave pseudo terminals master pseudo terminals slave pseudo terminals configuration file for inetd(1M) list of equivalent hosts user's private equivalence list temporary mount points for remote file systems where xxxxx is a string of alpha numeric characters. AUTHOR
was developed by Sun Microsystems, Inc. SEE ALSO
on(1), inetd(1M), mount(1M), dfstab(4), inetd.conf(4), inetd.sec(4). Using and Administering NFS Services rexd(1M)
