GEN:SID 1:582
Message RPC portmap rexd request UDP
Summary This event is generated when an attempt is made through a portmap GETPORT request to discover the port where the Remote Procedure Call (RPC) rexd is listening.
Impact Information disclosure.  This request is used to discover which port rexd is using.  Attackers can also learn what versions of the rexd protocol are accepted by rexd.
Detailed Information The portmapper service registers all RPC services on UNIX hosts. It can be queried to determine the port where RPC services such as rexd run.  The rexd RPC service allows remote program execution.  If weak authentication is used, an attacker may run arbitrary commands as a user other than root.
Affected Systems AIX 4.0
Compaq Tru64 UNIX (Any version)
HP-UX 10.20
HP-UX 11
Red Hat Linux 6.0
Red Hat Linux 7.x
Solaris 2.5.1
Solaris 2.6
Solaris 7
Solaris 8
Attack Scenarios An attacker can query the portmapper to discover the port where rexd runs.  This may be a precursor to accessing rexd.
Ease of Attack Simple.  
Corrective Action Limit remote access to RPC services.

Filter RPC ports at the firewall to ensure access is denied to RPC-enabled machines.

Disable unneeded RPC services.
Additional References Bugtraq
http://www.securityfocus.com/bid/37

CERT
http://www.cert.org/advisories/CA-1992-05.html

Arachnids
http://www.whitehats.com/info/IDS23

Rule References arachnids: 23