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Category:   Application (Generic)  >   Telnet Vendors:   [Multiple Authors/Vendors]
(Red Hat Issues Fix) Telnet Daemons May Give Remote Users Root Level Access Privileges
SecurityTracker Alert ID:  1002178
SecurityTracker URL:
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Date:  Aug 11 2001
Impact:   Execution of arbitrary code via network, Root access via network, User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   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 [2345].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.

Impact:   A remote user can execute arbitrary code on the server with the privileges of the telnet server, which is typically root level privileges.
Solution:   The vendor has released a fix. See the Source Message for the vendor's advisory containing directions on how to obtain the appropriate fix.
Cause:   Boundary error
Underlying OS:  Linux (Red Hat Linux)
Underlying OS Comments:  many Linux and Unix OSs are vulnerable, but not all - see the Alert text for more information

Message History:   This archive entry is a follow-up to the message listed below.
Jul 18 2001 Telnet Daemons May Give Remote Users Root Level Access Privileges

 Source Message Contents

Subject:  [RHSA-2001:099-06] New telnet packages available to fix buffer overflow vulnerabilities

                   Red Hat, Inc. Red Hat Security Advisory

Synopsis:          New telnet packages available to fix buffer overflow vulnerabilities
Advisory ID:       RHSA-2001:099-06
Issue date:        2001-08-02
Updated on:        2001-08-09
Product:           Red Hat Linux
Keywords:          telnet buffer overflow
Cross references:  

1. Topic:

New telnet, telnet-server packages are available for Red Hat Linux 5.2, 
6.2, 7.0 and 7.1. 
These packages fix a problem where buffer overflows can provide root 
access to local users.

It is recommended that all users update to the fixed packages.

2. Relevant releases/architectures:

Red Hat Linux 5.2 - alpha, i386, sparc

Red Hat Linux 6.2 - alpha, i386, sparc

Red Hat Linux 7.0 - alpha, i386

Red Hat Linux 7.1 - alpha, i386, ia64

3. Problem description:

4. Solution:

Before applying this update, make sure all previously released errata
relevant to your system have been applied.

To update all RPMs for your particular architecture, run:

rpm -Fvh [filenames]

where [filenames] is a list of the RPMs you wish to upgrade.  Only those
RPMs which are currently installed will be updated.  Those RPMs which are
not installed but included in the list will not be updated.  Note that you
can also use wildcards (*.rpm) if your current directory *only* contains the
desired RPMs.

Please note that this update is also available via Red Hat Network.  Many
people find this an easier way to apply updates.  To use Red Hat Network,
launch the Red Hat Update Agent with the following command:


This will start an interactive process that will result in the appropriate
RPMs being upgraded on your system.

5. Bug IDs fixed ( for more info):

50335 - telnetd segfaults during session negotiation

6. RPMs required:

Red Hat Linux 5.2:





Red Hat Linux 6.2:





Red Hat Linux 7.0:




Red Hat Linux 7.1:





7. Verification:

MD5 sum                           Package Name
b3e43fdd61e66fdf92b1c12dfbc25b1b 5.2/en/os/SRPMS/telnet-0.17.5x-18.src.rpm
23b34e59f5abc3d6f336f4bcaf2cfc94 5.2/en/os/alpha/telnet-0.17.5x-18.alpha.rpm
c075640ce8b75d1428c67c71cb08916e 5.2/en/os/i386/telnet-0.17.5x-18.i386.rpm
c13e1c86ef08363ed317550e2e87429f 5.2/en/os/sparc/telnet-0.17.5x-18.sparc.rpm
65a4919d0145366c84b2b758747153f5 6.2/en/os/SRPMS/telnet-0.17.6x-18.src.rpm
adb09756c21b4b920c47896b10263a52 6.2/en/os/alpha/telnet-0.17.6x-18.alpha.rpm
fc7d07585a065fbce46a35374a65c036 6.2/en/os/alpha/telnet-server-0.17.6x-18.alpha.rpm
cda5430e3ea6d337fbdb5d7284bbe404 6.2/en/os/i386/telnet-0.17.6x-18.i386.rpm
3222d7d4cc431ca93af62b491330d17c 6.2/en/os/i386/telnet-server-0.17.6x-18.i386.rpm
f4bfa409ecf232b5a16dee770a1d42ea 6.2/en/os/sparc/telnet-0.17.6x-18.sparc.rpm
4a78871d19f2cfebb22c29e1dd520f36 6.2/en/os/sparc/telnet-server-0.17.6x-18.sparc.rpm
5ca95a0c67a627406687e2059d62231d 7.0/en/os/SRPMS/telnet-0.17-18.src.rpm
4240f534045e52321cdfbb09e2079e67 7.0/en/os/alpha/telnet-0.17-18.alpha.rpm
a4119b8f0341eaf057c6ae5d8d429255 7.0/en/os/alpha/telnet-server-0.17-18.alpha.rpm
b3a99b8783a1a1691e72aaad460ed980 7.0/en/os/i386/telnet-0.17-18.i386.rpm
dbf205157cdaf3295cb62d4e3f6a2407 7.0/en/os/i386/telnet-server-0.17-18.i386.rpm
5ca95a0c67a627406687e2059d62231d 7.1/en/os/SRPMS/telnet-0.17-18.src.rpm
4240f534045e52321cdfbb09e2079e67 7.1/en/os/alpha/telnet-0.17-18.alpha.rpm
a4119b8f0341eaf057c6ae5d8d429255 7.1/en/os/alpha/telnet-server-0.17-18.alpha.rpm
b3a99b8783a1a1691e72aaad460ed980 7.1/en/os/i386/telnet-0.17-18.i386.rpm
dbf205157cdaf3295cb62d4e3f6a2407 7.1/en/os/i386/telnet-server-0.17-18.i386.rpm
c5134322a906709639a3885014462bf9 7.1/en/os/ia64/telnet-0.17-18.ia64.rpm
ad6090dbfbd9140eb77a26316de17300 7.1/en/os/ia64/telnet-server-0.17-18.ia64.rpm

These packages are GPG signed by Red Hat, Inc. for security.  Our key
is available at:

You can verify each package with the following command:
    rpm --checksig  <filename>

If you only wish to verify that each package has not been corrupted or
tampered with, examine only the md5sum with the following command:
    rpm --checksig --nogpg <filename>

8. References:

Copyright(c) 2000, 2001 Red Hat, Inc.

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