JBells is a trojan embedded into malformed MP3 files. The trojan uses a vulnerability in mpg123 which is a command-line MP3 player for Linux and other *NIX systems. When the trojanized MP3 is played with a vulnerable version of mpg123 a routine is started that deletes the current user's home directory and it's content.
The latest development version of mpg123 (0.59s) was tested and found to be vulnerable to this attack, while the latest stable version (0.59r) is not vulnerable.
The original exploit code generates ready to distribute trojanized MP3s for Suse 8.0 and Slackware 8.0 distributions.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
The exploit code generates an MP3 file with malformed header that causes a buffer overflow in mpg123's header parsing code. The malicious buffer is constructed so that it calls a command shell with a one-line command that removes the user's home directory recursively.
Even though the original exploit contains settings for the distributions mentioned above it is unfortunately easy to modify the exploit code to affect other Linux distributions and versions as well. Because of this users of vulnerable mpg123 versions are advised to change their mpg123 to a non-vulnerable version, regardless of their distribution.
Technical Details: Gergely Erdelyi; F-Secure Corp.; January 15th, 2003