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"By creating a crontab that runs with a specially formatted 'MAILTO' environment variable, it is possible for local users to overflow a fixed-length buffer in the cron daemon's cron_popen() function. Since the cron daemon runs as root, it would be theoretcially possible for local users to use this buffer overflow to gain root privilege."

Date: Wed, 25 Aug 1999 21:17:20 -0400
From: Bill Nottingham @redhat.com
To: redhat-watch-list@redhat.com

Synopsis: Buffer overflow in cron daemon
Advisory ID: RHSA-1999:030-01
Issue date: 1999-08-25
Updated on:
Keywords: vixie-cron crond MAILTO
Cross references:

1. Topic:

A buffer overflow exists in crond, the cron daemon. This could allow local users to gain privilege.

2. Bug IDs fixed (http://developer.redhat.com/bugzilla/):

4706

3. Relevant releases/architectures:

Red Hat Linux 4.2, 5.2, 6.0, all architectures

4. Obsoleted by:

5. Conflicts with:

6. RPMs required:

Red Hat Linux 4.2:

Intel:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/4.2/i386/vixie-cron-3.0.1-36.4.2.i386.rpm

Alpha:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/4.2/alpha/vixie-cron-3.0.1-36.4.2.alpha.rpm

Sparc:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/4.2/sparc/vixie-cron-3.0.1-36.4.2.sparc.rpm

Source packages:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/4.2/SRPMS/vixie-cron-3.0.1-36.4.2.src.rpm

Red Hat Linux 5.2:

Intel:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/5.2/i386/vixie-cron-3.0.1-36.5.2.i386.rpm

Alpha:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/5.2/alpha/vixie-cron-3.0.1-36.5.2.alpha.rpm

Sparc:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/5.2/sparc/vixie-cron-3.0.1-36.5.2.sparc.rpm

Source packages:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/5.2/SRPMS/vixie-cron-3.0.1-36.5.2.src.rpm

Red Hat Linux 6.0:

Intel:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/6.0/i386/vixie-cron-3.0.1-37.i386.rpm

Alpha:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/6.0/alpha/vixie-cron-3.0.1-37.alpha.rpm

Sparc:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/6.0/sparc/vixie-cron-3.0.1-37.sparc.rpm

Source packages:
rpm -Uvh ftp://ftp.redhat.com/redhat/updates/6.0/SRPMS/vixie-cron-3.0.1-37.src.rpm

7. Problem description:

By creating a crontab that runs with a specially formatted 'MAILTO' environment variable, it is possible for local users to overflow a fixed-length buffer in the cron daemon's cron_popen() function. Since the cron daemon runs as root, it would be theoretcially possible for local users to use this buffer overflow to gain root privilege.

To the best of our knowledge, no known exploits exist at this time.

Also, it was possible to use specially formatted 'MAILTO' environment variables to send commands to sendmail.

8. Solution:

For each RPM for your particular architecture, run:

rpm -Uvh

where filename is the name of the RPM.

9. Verification:

MD5 sum Package Name

a90bf7adbc719fdb5a8ed335fda32a3c  i386/vixie-cron-3.0.1-36.4.2.i386.rpm
2b6b0b00cdeca0381ab2893ddf2f2bd1  alpha/vixie-cron-3.0.1-36.4.2.alpha.rpm
02d183979b594a7e7a9c1bc8566b2f16  sparc/vixie-cron-3.0.1-36.4.2.sparc.rpm
b8ac0c21e108ebd67925c224f7a0b82b  SRPMS/vixie-cron-3.0.1-36.4.2.src.rpm

7df6884f0709b078d19f390db2a7e304  i386/vixie-cron-3.0.1-36.5.2.i386.rpm
b51b4ea612c4f5a59c1bb4e76af95eeb  alpha/vixie-cron-3.0.1-36.5.2.alpha.rpm
5ceeb614442bd4d4ce8a9680664d77e4  sparc/vixie-cron-3.0.1-36.5.2.sparc.rpm
9f411cb3c7c1c53423eebc9d5f64619a  SRPMS/vixie-cron-3.0.1-36.5.2.src.rpm

39bbedeade7dc6da6f0ab5acfb3af6da  i386/vixie-cron-3.0.1-37.i386.rpm
addec82afbd131aef14fadf8cfb8ddcf  alpha/vixie-cron-3.0.1-37.alpha.rpm
b56db77c411f72825efbffed43780213  sparc/vixie-cron-3.0.1-37.sparc.rpm
243d9099bdb94bd0d075de4da4dbba12  SRPMS/vixie-cron-3.0.1-37.src.rpm

These packages are PGP signed by Red Hat Inc. for security. Our key is available at:

http://www.redhat.com/corp/contact.html

You can verify each package with the following command:

rpm --checksig

If you only wish to verify that each package has not been corrupted or tampered with, examine only the md5sum with the following command:

rpm --checksig --nopgp

10. References: