rexecd - The remote execution server
rexecd [-s]
Causes rexecd to check for the ptys keyword in the
/etc/securettys file and to deny execution of the request
if it is from root and on a pseudoterminal.
The rexecd daemon is the server for the rexec(3) routine.
The server provides remote execution facilities with
authentication based on usernames and passwords.
The rexecd daemon listens for service requests at the port
indicated in the exec service specification; see services(4). When a service request is received, the following
protocol is initiated: The server reads characters
from the socket up to a null (`\0') byte. The resultant
string is interpreted as an ASCII number, base 10. If the
number received in step 1 is nonzero, it is interpreted as
the port number of a secondary stream to be used for the
stderr. A second connection is then created to the specified
port on the client's machine. A null-terminated
username of at most 16 bytes is retrieved on the initial
socket. A null-terminated, unencrypted password of at
most 80 bytes is retrieved on the initial socket. A nullterminated
command to be passed to a shell is retrieved on
the initial socket. The length of the command is limited
by the upper bound on the size of the system's argument
list. The rexecd server then validates the user as is
done at login time and, if started with the -s option,
verifies that the /etc/securettys file is not setup to
deny the user. If the authentication was successful, rexecd
changes to the user's home directory, and establishes
the user and group protections for the user. If any of
these steps fail, the connection is aborted with a diagnostic
message returned. A null byte is returned on the
initial socket and the command line is passed to the normal
login shell of the user. The shell inherits the network
connections established by rexecd.
Except for the last diagnostic message listed, all diagnostic
messages are returned on the initial socket, after
which any network connections are closed. An error is
indicated by a leading byte with a value of 1 (0 is
returned in step 7 above upon successful completion of all
the steps prior to the command execution). The name is
longer than 16 bytes. The password is longer than 80
bytes. The command line passed exceeds the size of the
argument list (as configured into the system). No password
file entry for the username existed. The wrong password
was supplied. The chdir command to the home directory
failed. A fork by the server failed. The user's
login shell could not be started. This message is returned
on the connection associated with stderr and is not preceded
by a option byte.
Indicating Login incorrect as opposed to Password incorrect
is a security breach that allows people to probe a
system for users with null passwords.
Specifies the command path
Functions: rexec(3)
Files: securettys(4)
rexecd(8)
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