Mambo Exploit Blocked by SELinux
Listing 5. Investigating File Timestamps
$ for x in atime access status use; do > echo -n "$x " > ls -l --time=$x /tmp/cback > done [rbulling@targetbox ~]$ for x in atime access status use mtime; do > echo -n "$x " ; ls -l --time=$x /tmp/cback > done atime -rwxr--r-- 1 apache apache 13901 May 6 11:33 /tmp/cback access -rwxr--r-- 1 apache apache 13901 May 6 11:33 /tmp/cback status -rwxr--r-- 1 apache apache 13901 May 4 07:52 /tmp/cback use -rwxr--r-- 1 apache apache 13901 May 6 11:33 /tmp/cback
The cback binary probably was created at 07:52 AM on May 4, corresponding to the wget command injection attack. That was the last time the file attributes were modified. Although UNIX does not allow you to retrieve the true creation time of a file, the status time often can stand in for that. The other times correspond to the times of my own initial investigations of the cback file. If I had been more careful, I could have done this ls command before reading the cback file at all, so that the atime, access and use times would have been those the attacker had set.
Because this looked like a worm attacking Mambo, a search on “mambo worm” on Google found references to the attack, including articles from ComputerWorld, Outpost24, F-Secure and Bugtraq (see Resources).
The Mitre Common Vulnerabilities and Exposures Project provides a dictionary of known vulnerabilities. It has a brief abstract of the characteristics of the vulnerability with references to security mailing lists and Web sites that confirm the problems. Searching for “mambo” on www.cvw.mitre.org yielded a couple-dozen known vulnerabilities—one of which (CVS-2005-3738) relates to mosConfig_absolute_path, one of the seriously mangled variables in the request URL.
After reading up on recent malware activity surrounding Mambo, I saw that the attack vector probably was closely related to the Net-Worm.Linux.Mare.d worm strain described in the news reports and vulnerability databases. However, some of the names of executables in the attack that hit targetbox were slightly different from the attack executables named in the vulnerability reports.
To run these security analysis tools in the safest way possible, you need to disconnect the computer in question from all networks and boot from known good media before attempting to analyze the intrusion. That way, any remaining attack programs will not be able to attack other machines on your network, and intruders will not interrupt your investigation by interacting with the machine. You won't be able to use the system while you analyze the intrusion, and it may take time to put together an analysis toolkit that will work on a rescue disk. Although this takes more time and preparation than running the analysis tools on a running system that might be compromised, it gives a higher level of assurance that a compromise will not spread to other machines on your network.
Making a backup copy of the entire disk to a removable drive also is a good idea. You could use a command such as this to do the job:
# dd if=/dev/hda1 of=/mnt/removable-drive/disk.img bs=512k
You then can mount and analyze the backup using the loop device (see “Disk Images under Linux” in the Resources section). It's probably faster and easier to analyze the original system, but it's nice to have this backup for forensic purposes.
In an ideal world, you could do this the moment you realize an attack has succeeded. However, sometimes you have to assess the severity of the compromise and balance that against the time and resources you have available.
It looks like whoever broke in could have read or written to any file available to the apache user. This would include the PHP configuration file for Mambo that had a MySQL database user name and password in it. I changed that password just to be sure that the intruder could not use it to attempt further privilege escalation.
Fortunately for me, this was only a test installation, so to prevent future exploits, I removed the Mambo installation completely. I also could have attempted to upgrade the software to remove the vulnerability.
When a user account is compromised, you need to face the danger that the attacker could gain access to the superuser (root) account. If an attacker gets root, it can make it much more difficult to recover from an attack. Most of the time, you need to re-install the operating system from known good media and carefully and selectively audit and restore software configurations. Attackers who manage to get root access often install a rootkit—software that hides itself from casual inspection and offers a remote control back door or other malicious features. Fortunately, a program called chkrootkit (from chkrootkit.org) can help scan for active rootkits. Listing 6 shows the output of chkrootkit in quiet mode on targetbox.
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