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Secure Networks Inc.
Security Advisory
October 21, 1997
in.telnetd tgetent buffer overflow
This advisory addresses a vulnerability in the tgetent(3) library
routine which allows an attacker to obtain root privileges by connecting
to a vulnerable system's telnet daemon.
Problem Description
~~~~~~~~~~~~~~~~~~~
A vulnerability in the tgetent(3) library routine can result in a
buffer overflow in the telnet daemon on some BSD derived systems. By
uploading an alternate terminal capability database, an attacker
can exploit this vulnerability to gain unauthorized super-user access
to a vulnerable system, or to gain super-user access on a system
which they already have access to.
This problem can be exploited by mailing a file into the system, or
uploading a file via FTP. Once this file has been transferred to the
remote system, the attacker must only be able to connect to the telnet
daemon, to obtain super-user access.
Technical Details
~~~~~~~~~~~~~~~~~
The tgetent(3) library call requires the passing in of a buffer in
which the terminal entry is stored.
/*
* Get an entry for terminal name in buffer bp from the termcap file.
*/
int
tgetent(bp, name)
char *bp, *name;
{
The tgetent(3) library call does no checking on the size of data which
is placed into the *bp buffer. Many programs pass in a buffer of size
1024 bytes. By creating a termcap terminal specification larger than
1024 bytes, we can overflow a buffer in the calling function. If this
buffer is stored on the stack in the calling function, we can cause
arbitrary machine code to be executed.
The BSD telnet daemon calls the tgetent(3) function as follows:
char buf[1024];
if (terminaltype == NULL)
return(1);
if (tgetent(buf, s) == 0)
return(0);
return(1);
By specifying a terminal capability entry which is larger than 1024
bytes, an overflow occurs in the telnet daemon, allowing arbitrary
machine instructions to be executed.
Impact
~~~~~~
Remote individuals can obtain super-user access to any vulnerable system.
This vulnerability can allow remote users to obtain super-user access on
vulnerable systems, and can allow local users to obtain super-user access.
Vulnerable Systems
~~~~~~~~~~~~~~~~~~
BSD/OS (BSDI)
Version 2.1 of BSD/OS is vulnerable
Version 3.0 of BSD/OS is NOT vulnerable
BSDI has issued a security fix which is currently in the testing
phases and will be availible at the following location:
ftp://ftp.bsdi.com/bsdi/patches/patches-2.1/U210-043
Solaris 2.x
Solaris 2.x is NOT vulnerable to this problem
AIX
AIX is NOT vulnerable to this problem
HP-UX
HP-UX is NOT vulnerable to this problem
Linux
The current versions of Linux which were tested include Slackware
and Redhat, which appear to be NOT vulnerable.
IRIX
IRIX appears to be NOT vulnerable.
NetBSD
Current versions of NetBSD are not vulnerable.
FreeBSD
Versions of FreeBSD newer than 2.1.5 are NOT vulnerable to this
problem. FreeBSD-current, FreeBSD 2.1.7 and FreeBSD 2.2.2 are NOT
vulnerable.
OpenBSD
Versions of OpenBSD newer than 2.0 are NOT vulnerable to this problem.
Additional Information
~~~~~~~~~~~~~~~~~~~~~~
This problem was discovered by Theo de Raadt <deraadt@openbsd.org>
You can contact Secure Networks Inc. at <sni@secnet.com> using
the following PGP key:
Type Bits/KeyID Date User ID
pub 1024/9E55000D 1997/01/13 Secure Networks Inc. <sni@secnet.com>
Secure Networks <security@secnet.com>
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Copyright Notice
~~~~~~~~~~~~~~~~
The contents of this advisory are Copyright (C) 1997 Secure Networks Inc,
and may be distributed freely provided that no fee is charged for
distribution, and that proper credit is given.
You can find Secure Networks papers at ftp://ftp.secnet.com/pub/papers
and advisories at ftp://ftp.secnet.com/advisories
You can browse our web site at http://www.secnet.com
You can subscribe to our security advisory mailing list by sending mail to
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