tcpd - access control facility for internet services
The tcpd program can be set up to monitor incoming requests for telnet, finger, ftp, exec, rsh, rlogin, tftp, talk, comsat and other ser-
vices that have a one-to-one mapping onto executable files.
The program supports both 4.3BSD-style sockets and System V.4-style TLI. Functionality may be limited when the protocol underneath TLI is
not an internet protocol.
Operation is as follows: whenever a request for service arrives, the inetd daemon is tricked into running the tcpd program instead of the
desired server. tcpd logs the request and does some additional checks. When all is well, tcpd runs the appropriate server program and goes
Optional features are: pattern-based access control, client username lookups with the RFC 931 etc. protocol, protection against hosts that
pretend to have someone elses host name, and protection against hosts that pretend to have someone elses network address.
The same monitoring and access control functionality provided by the tcpd standalone program is also available through the libwrap shared
library interface. Some programs, including the Solaris inetd daemon, have been modified to use the libwrap interface and thus do not
require replacing the real server programs with tcpd. The libwrap interface is also more efficient and can be used for inetd internal ser-
vices. See inetd(1M) for more information.
Connections that are monitored by tcpd are reported through the syslog(3) facility. Each record contains a time stamp, the client host name
and the name of the requested service. The information can be useful to detect unwanted activities, especially when logfile information
from several hosts is merged.
In order to find out where your logs are going, examine the syslog configuration file, usually /etc/syslog.conf.
Optionally, tcpd supports a simple form of access control that is based on pattern matching. The access-control software provides hooks
for the execution of shell commands when a pattern fires. For details, see the hosts_access(4) manual page.
HOST NAME VERIFICATION
The authentication scheme of some protocols (rlogin, rsh) relies on host names. Some implementations believe the host name that they get
from any random name server; other implementations are more careful but use a flawed algorithm.
tcpd verifies the client host name that is returned by the address->name DNS server by looking at the host name and address that are
returned by the name->address DNS server. If any discrepancy is detected, tcpd concludes that it is dealing with a host that pretends to
have someone elses host name.
If the sources are compiled with -DPARANOID, tcpd will drop the connection in case of a host name/address mismatch. Otherwise, the host-
name can be matched with the PARANOID wildcard, after which suitable action can be taken.
HOST ADDRESS SPOOFING
Optionally, tcpd disables source-routing socket options on every connection that it deals with. This will take care of most attacks from
hosts that pretend to have an address that belongs to someone elses network. UDP services do not benefit from this protection. This feature
must be turned on at compile time.
When RFC 931 etc. lookups are enabled (compile-time option) tcpd will attempt to establish the name of the client user. This will succeed
only if the client host runs an RFC 931-compliant daemon. Client user name lookups will not work for datagram-oriented connections, and
may cause noticeable delays in the case of connections from PCs.
Warning: If the local system runs an RFC 931 server it is important that it be configured NOT to use TCP Wrappers, or that TCP Wrappers be
configured to avoid RFC 931-based access control for this service. If you use usernames in the access control files, make sure that you
have a hosts.allow entry that allows the RFC 931 service (often called "identd" or "auth") without any username restrictions. Failure to
heed this warning can result in two hosts getting in an endless loop of consulting each other's identd services.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Availability | SUNWtcpd |
|Interface Stability | Committed |
Source for tcp_wrappers is available in the SUNWtcpdS package.