If you haven't heard yet, there is a major security hole in all versions of Send Mail except for the most recent version. By simply sending a carefully crafted email, anybody can take root priviledges on any server that is vulnerable. This is
very bad news as the internet as a whole mostly uses Send Mail for mail service. That means that an extremely high percentage of servers internet wide are vulnerable. Once a server is "taken" and a root kit is applied, it can be used for ANYTHING including pr0n servers or data mining of private information INCLUDING such things as credit card info and social security information!
Researchers at Internet Security Systems (ISS) have discovered a remotely exploitable vulnerability in sendmail. This vulnerability could allow an intruder to gain control of a vulnerable sendmail server.
Most organizations have a variety of mail transfer agents (MTAs) at various locations within their network, with at least one exposed to the Internet. Since sendmail is the most popular MTA, most medium-sized to large organizations are likely to have at least one vulnerable sendmail server. In addition, many UNIX and Linux workstations provide a sendmail implementation that is enabled and running by default.
This vulnerability is message-oriented as opposed to connection-oriented. That means that the vulnerability is triggered by the contents of a specially-crafted email message rather than by lower-level network traffic. This is important because an MTA that does not contain the vulnerability will pass the malicious message along to other MTAs that may be protected at the network level. In other words, vulnerable sendmail servers on the interior of a network are still at risk, even if the site's border MTA uses software other than sendmail. Also, messages capable of exploiting this vulnerability may pass undetected through many common packet filters or firewalls.
Sendmail has indicated to the CERT/CC that this vulnerability has been successfully exploited in a laboratory environment. We do not believe that this exploit is available to the public. However, this vulnerability is likely to draw significant attention from the intruder community, so the probability of a public exploit is high.
read more here:
http://www.cert.org/advisories/CA-2003-07.html
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