(Caldera Issues Fix) Telnet Daemons May Give Remote Users Root Level Access Privileges
SecurityTracker Alert ID: 1002066|
SecurityTracker URL: http://securitytracker.com/id/1002066
(Links to External Site)
Date: Jul 23 2001
Execution of arbitrary code via network, Root access via network, User access via network|
Fix Available: Yes Vendor Confirmed: Yes |
TESO reported that many BSD-derived Telnet daemons (servers) contain a vulnerability that may allow a remote user to obtain root level access on the server.|
The vulnerability is reportedly due to a buffer overflow in the telnet option handling.
The following systems are reported to be vulnerable:
BSDI 4.x default, FreeBSD .x default, IRIX 6.5, Linux netkit-telnetd < 0.14, NetBSD 1.x default, OpenBSD 2.x, Solaris 2.x sparc, and "almost any other vendor's telnetd".
A remote user can send a specially formatted option string to the remote telnet server and overwrite sensitive memory, causing arbitrary code to be executed with the privileges of the telnet server (which is typically root level privileges).
Telnet options are reportedly processed by the 'telrcv' function. The results of the parsing, which are to be send back to the client, are stored in the 'netobuf' buffer. It is apparently assumed that the reply data is smaller than the buffer size, so no bounds checking is performed. By using a combination of options, especially the 'AYT' Are You There option, it is possible for a remote user to append data to the buffer. It is reported that the characters that can be written to the buffer are limited, which makes constructing a successful exploit difficult.
The report states that a working exploit has been developed for BSDI, NetBSD and FreeBSD. However, the exploit was not released.
A remote user can execute arbitrary code on the server with the privileges of the telnet server, which is typically root level privileges.|
The vendor has released a fix. See the Source Message for the vendor's advisory containing directions on how to obtain the appropriate fix.|
|Underlying OS: Linux (Caldera/SCO)|
|Underlying OS Comments: many Linux and Unix OSs are vulnerable, but not all - see the Alert text for more information|
This archive entry is a follow-up to the message listed below.|
Source Message Contents
Subject: (Non) Vulnerability in telnetd|
Content-Type: text/plain; charset=us-ascii
A vulnerability in all BSD derived implementations of the TELNET server
daemon was published during the weekend that allows attackers to gain
root privilege on the attacked machine.
This bug has been present in the Linux port of telnetd up to and including
The only (supported) OpenLinux product that would be vulnerable to this
bug are OpenLinux 2.3 and OpenLinux eServer 2.3. However, we did release
a security update for these in March 2000 that brought the netkit-telnet
package to version 0.16, which is not vulnable anymore.
We therefore encourage all users of OpenLinux 2.3 and eServer 2.3 to
apply this security patch if they haven't already done so. The fixes
are available from
OpenLinux eServer 2.3:
Olaf Kirch | --- o --- Nous sommes du soleil we love when we play
firstname.lastname@example.org | / | \ sol.dhoop.naytheet.ah kin.ir.samse.qurax
email@example.com +-------------------- Why Not?! -----------------------
UNIX, n.: Spanish manufacturer of fire extinguishers.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.5 (GNU/Linux)
Comment: For info see http://www.gnupg.org
-----END PGP SIGNATURE-----