Hacking Unix/Linux

Footprinting, Scanning, Enumeration Footprinting: Similar to Windows but using different tools: Network enumeration: using whois and finding authoritative name server. DNS interrogation: using nslookup for zone transfer , host to find e-mail server, and traceroute for network reconnaissance. Also dig. Ubuntu: use System, Administration, Network Tools for ping, whois, traceroute, etc. Scanning: again similar to Windows with different tools : Nmap and Nmapfe: use sudo apt-get install nmap and sudo apt-get install nmapfe to setup. Use sudo nmapfe for graphical interface. ping sweeps, port scanning: tcp and udp, OS detection. Countermeasures: Snort and Psionic Port Sentry: documentation. (seen later in IPS/IDS) Enumeration: UNIX enumeration. UNIX Users and group enumeration: finger (see this example) and tftp should be disabled and killed. Basic daemons: sendmail, rpc, NFS, NIS -- all have known vulnerabilities, setup and latest security patches should be applied carefully.

Getting started Vulnerability mapping: identify specific software vulnerabilities (e.g. sendmail, telnet, ftp, NFS, apache). Quest for root: root or nothing ? Su - root. Remote access: gaining access via the network exploit a listening daemon/service a UNIX system performing routing with IP forwarding enabled user-initiated remote execution (hostile Web site, Trojan horses, etc) Local access: having access to a shell or login to the system privilege escalation attacks (from login to root) once a remote access exploits a vulnerability it gains local shell access Brute force attacks: (we will see John the Ripper but not Hydra) remote login programs: telnet, ftp, rlogin.rsh,ssh, http plus a tool to crack the username/password combination. The /etc/passwd file. You should use shadow passwords. Countermeasures: password education and software (e.g. checkpassd)

Remote access Data driven attacks: sending data to an active service that causes unintended results, generally allowing access to the system Buffer Overflow: same Windows vulnerabilities (C programs). Countermeasures: basically good programming practices, testing, auditing, safer compilers, etc. Input Validation: failure in validating input and accepting extraneous input (hack code!!!). Produces similar results to buffer overflow and the countermeasure is the same: safe programming. Shell access: after gaining access using a data driven attack the first objective is to open a shell window to enter commands. Traditional shell access: telnet, rlogin,ssh (admins can close most). Using X-Windows to run xterm in the remote (target) machine and display in the intruder machine, using its client/server features. Reverse telnet and back channels: admins can remove X, then what? Run nc (netcat) in the intruder and run malicious code in the target creating a telnet connection from target to intruder. Countermeasures: remove X (servers), chmod 750 telnet (Linux, root only), better yet only use ssh.

Common remote access attacks FTP: do not run anonymous FTP in the same server you have regular accounts and ftp with user authentication. Keep up to date with vulnerabilities (e.g. wu-ftpd, a popular ftp, had a vulnerability in exec). Better yet, only use ssh/scp. Sendmail: a very complex mail server (over 80,000 lines of code), which few understand. It is needed in almost all UNIX machines and in most cases should not be disabled. Qmail is a potential replacement. Remote Procedure Call: rpcinfo (as root) let us see the running rpc services. Best defense is to limit the use of RPC services to the minimum. NFS: do not export the file system to everyone, or enable NFS selectively (not active in the MISLab), files saved locally, not in the network. DNS: disable BIND in machines NOT used as DNS servers (type ps aux to see what processes are running, also look for /etc/name.boot). Discussing named is beyond the scope of this course (another difficult daemon to setup safely). Test for buffer overflow using dig @ipnumber version.bind chaos txt X Windows: use xhost to add, delete, names and hosts which can access X-Windows. Not a strong line of defense. Again, remove X-Windows from servers

Local access Password cracking: We cannot decrypt a password, we use a dictionary, or other type of algorithm to generate passwords, encrypt them using the crypt function, DES, etc, and compare with hash in the passwd file. Crack 5 and John the Ripper are two of “the best of the breed.” Local buffer overflow: same problems and countermeasures. Symlinks: ln -s /this /that, when you cat this you see that. Signals in UNIX: you re-start, start, stop daemons sending signals: SIGXXX. Core dump: memory (core) dumps are snapshots of the memory when an error occurs. Delete it or it stays. ulimit set to 0 cancel core dumps. Shared libraries: replace a standard library file with a rogue one, granting privileges to the intruder, when used. Kernel problems: upgrades to the kernel may create security flaws, which will be found, patched, etc. Linux particularly vulnerable (growing). File and directory permissions: SUID files -- a necessary evil. Some applications need to run as root and be used by regular users (solution: SUID). The find command list these files, and there are many of them. World writable files are another problem.