Chapter 2. Attackers and Risks

21

between the remote service and the unsuspecting user capturing information. This way a cracker can

gather administrative passwords and raw data without either the server's or the user's knowledge.

Another example of insecure services are network file systems and information services such as NFS

or NIS which are developed explicitly for LAN usage but are, unfortunately, extended to include

WANs (for remote users). NFS does not, by default, have any authentication or security mechanisms

configured that will prevent a cracker from simply mounting the NFS share and accessing anything

contained therein. NIS, as well, has vital information that must be known by every computer on

a network, including passwords and file permissions, within a plain text ACSII or DBM (ASCII 

derived) database. A cracker can take this database and find the passwords of each and every user on

a network, including the administrator.

2.4. Threats To Workstation and Home PC Security

Workstations and home PCs may not be as prone to attack as networks or servers, but they may contain

sensitive information, such as credit card information, that would be damaging if stolen. They may

also be used by attackers as a "slave" machine in coordinated attacks, without the user's knowledge.

Knowing the vulnerabilities of your workstation can save you the headache of having to reinstall your

operating system   or having your administrator do it for you.

2.4.1. Bad Passwords

Bad passwords are not invalid when running Red Hat Linux. However, a bad password is one of the

easiest ways for an attacker to gain access to a system. For more on how to avoid common pitfalls

when creating a password, see Section 4.3.

2.4.2. Vulnerable Client Applications

Although an administrator may have a fully secure and patched server, that does not mean that remote

users are secure when accessing it. For instance, if the server offers Telnet or FTP services over a

public network, an attacker can capture the plain text usernames and passwords as they pass over the

network, and then use the account information to access the remote user's workstation.

Even when using secure protocols, such as SHH, a remote user may be vulnerable to certain attacks

if they do not keep their client applications updated. For instance, v.1 SSH clients are vulnerable to

an X forwarding attack from malicious SSH servers. Once connected to the server, the attacker can

quietly capture any keystrokes and mouse clicks made by the client over the network. This problem

was fixed in the v.2 SSH protocol, but it is up to the user to keep track of what applications have such

vulnerabilities and update them as necessary.

Chapter 4 will discuss in more detail what steps administrators and home users should take to limit

the vulnerability of computer workstations.