PPPTalk is an administrative interface for the PPP subsystem. It controls the operation of the PPP daemon.
Attackers can gain super user privileges by exploiting a vulnerability in PPPTalk on systems running PPPD. The crux of the problem lies in that the effective user id is not reset before ppptalk starts the shell. By taking advantage of a shell escape feature in the ppptalk application an attacker can gain root privileges. The following is a snapshot of the exploit in action:
uid=0(root) gid=1(other) groups=0(root), 1(other), 2(bin), 3(sys), 4(adm), 5(uucp),
6(mail), 7(tty), 8(audit), 10(nuucp), 12(daemon), 23(cron), 25(dtadmin), 47(priv), 9(lp)
Any local user can launch this attack and obtain super user privileges. Successful exploitation is trivial and provides the attacker with full control over the target system.
iDEFENSE has proof of concept exploit code demonstrating the impact of this vulnerability.
Exploitation is possible if ppptalk is installed set user id root and pppd is running, both of these conditions are met on a default installation of The SCO Group's UnixWare.
Remove the setuid bit from the ppptalk binary by executing the following command:
# chmod -s `which ppptalk`
The vendor has provided the following fixes:
Caldera UnixWare 7.1.1:
Caldera Patch erg711697a.Z
Caldera OpenUnix 8.0:
Caldera Patch erg712071.pkg.Z
A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has assigned CAN-2002-0827 to this issue.
10/02/2002 Exploit acquired by iDEFENSE
10/05/2002 Initial vendor notification
10/08/2002 iDEFENSE Clients notified
10/15/2002 Public Disclosure
Texonet Co. is credited with this discovery.
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