|TCPD(8)||System Manager's Manual||TCPD(8)|
tcpdprogram can be set up to monitor incoming requests for telnet(1), finger(1), ftp(1), rsh(1), tftp(1), talk(1), comsat(8), and other services that have a one-to-one mapping onto executable files.
Operation is as follows: whenever a request for service arrives,
the inetd(8) daemon is tricked
into running the
tcpd program instead of the desired
tcpd logs the request and does some
additional checks. When all is well,
tcpd runs the
appropriate server program and goes away.
Optional features are: pattern-based access control, client username lookups with the RFC 931 etc. protocol, protection against hosts that pretend to have someone else's host name, and protection against hosts that pretend to have someone else's network address.
tcpdare 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.
tcpdsupports 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(5) manual page.
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.
tcpddisables 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 else's network. UDP services do not benefit from this protection. This feature must be turned on at compile-time.
tcpdwill 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.
tcpdexpects that the network daemons are left in their original place, as it is configured within OpenBSD.
finger stream tcp nowait nobody /usr/libexec/fingerd fingerd
finger stream tcp nowait nobody /usr/libexec/tcpd fingerd
Similar changes will be needed for the other services that are to
be covered by
tcpd. Send a `kill -HUP´ to the
inetd(8) process to make the
In the case of daemons that do not live in a common directory ("secret" or otherwise), edit the inetd(8) configuration file so that it specifies an absolute path name for the process name field. For example:
ntalk dgram udp wait root /usr/libexec/tcpd /usr/local/lib/ntalkd
Only the last component (
ntalkd) of the
pathname will be used for access control and logging.
Wietse Venema (email@example.com), Department of Mathematics and Computing Science, Eindhoven University of Technology Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
RPC broadcast requests (for example: rwall(1), rup(1), rusers(1)) always appear to come from the responding host. What happens is that the client broadcasts the request to all portmap(8) daemons on its network; each portmap(8) daemon forwards the request to a local daemon. As far as the rwalld(8) etc. daemons know, the request comes from the local host.
|May 31, 2007||OpenBSD-5.1|