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Vulnerability Note VU#569272System V derived login contains a remotely exploitable buffer overflowOverviewA remotely exploitable buffer overflow exists in implementations of login, derived from System V. An attacker can use this vulnerability to gain the privileges of the process that invoked login, user root in the cases of in.telnetd, or in.rlogind. We have been able to determine that several vendors are affected.I. DescriptionImplementations of login, derived from System V, use a fixed-size buffer to store environment and argument variables that are received from other programs. This buffer can be overflowed by inputing numerous variables. An attacker can use this vulnerability to gain the privileges of the process that invoked login. If an attacker with a local shell invokes login directly, they can only gain the privileges of the shell they already have. However, if the attacker can invoke login via a suid root program, such as the in.telnetd or in.rlogind daemons, they can gain the privileges of the invoking suid program, typically root. And of course, because in.telnetd and in.rlogind are available over the network, an attacker without any previous access to the system could use this vulnerability to gain root access directly.An exploit exists and may be circulating.
Disable telnet, rlogin, and other programs that use login for authentication. Use programs that use SSH instead and do not use login by default.
References
Our thanks to Mark Dowd and ISS for the report and information contained in their advisory and to Sun Microsystems for their help in identifing the location of the vulnerability. This document was written by Jason Rafail.
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