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Category:   Application (Generic)  >   Telnet Vendors:   [Multiple Authors/Vendors]
(Red Hat Issues Fixed Kerberos Package) Telnet Daemons May Give Remote Users Root Level Access Privileges
SecurityTracker Alert ID:  1002176
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 for Kerberos 5, which contains the affected telnet program. 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-2001:100-02] Updated Kerberos 5 packages now available

                   Red Hat, Inc. Red Hat Security Advisory

Synopsis:          Updated Kerberos 5 packages now available
Advisory ID:       RHSA-2001:100-02
Issue date:        2001-08-02
Updated on:        2001-08-09
Product:           Red Hat Linux
Keywords:          kerberos 5 telnet
Cross references:  
Obsoletes:         RHSA-2001:060

1. Topic:

Updated Kerberos 5 packages are now available for Red Hat Linux 6.2, 7,
and 7.1. These updates close vulnerabilities due to potential buffer
overflows in the Kerberos-aware telnet server included in the
krb5-workstation package.

2. Relevant releases/architectures:

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:

By exploiting buffer overflows in the telnet server included in the
krb5-workstation package, a remote attacker can obtain superuser privileges
on a vulnerable host.

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):

30697 - The ftp server doesn't handle large files
41911 - krb5-server-1.2.2-4 possible bad init script (missing reload)
42551 - Addition of "ANY" keytab type.
45965 - ksu prints syslog messages to stderr

6. RPMs required:

Red Hat Linux 6.2:





Red Hat Linux 7.0:




Red Hat Linux 7.1:





7. Verification:

MD5 sum                           Package Name
32c2b378d7e345c138d36e394f069b39 6.2/en/os/SRPMS/krb5-1.1.1-28.src.rpm
0dcd3c527aab3c963f1d2f675f3415c8 6.2/en/os/alpha/krb5-configs-1.1.1-28.alpha.rpm
2a665b9e15572f509cc62032df4609d5 6.2/en/os/alpha/krb5-devel-1.1.1-28.alpha.rpm
c9744248932d65e76ed8d8b5462e5779 6.2/en/os/alpha/krb5-libs-1.1.1-28.alpha.rpm
fa38f5c25164c6f9b79804e246c53425 6.2/en/os/alpha/krb5-server-1.1.1-28.alpha.rpm
b1313389a6f6511b5e05df003bf166e4 6.2/en/os/alpha/krb5-workstation-1.1.1-28.alpha.rpm
97ebbf14de88869c8b1b5b932f3fb920 6.2/en/os/i386/krb5-configs-1.1.1-28.i386.rpm
a57afb63eb62b15dafaf42d39fa809d7 6.2/en/os/i386/krb5-devel-1.1.1-28.i386.rpm
2186fafedfc49cd21bc2f0cad8b42186 6.2/en/os/i386/krb5-libs-1.1.1-28.i386.rpm
5195f7eab0efe095fcd1531495f5cb8f 6.2/en/os/i386/krb5-server-1.1.1-28.i386.rpm
94ce34d6d5fdaa4ce3113b96117c361d 6.2/en/os/i386/krb5-workstation-1.1.1-28.i386.rpm
f03782a1bb3456f103639265f1fce94a 6.2/en/os/sparc/krb5-configs-1.1.1-28.sparc.rpm
6fee7baeba6911112086fb130b13fcf4 6.2/en/os/sparc/krb5-devel-1.1.1-28.sparc.rpm
c238a3ab7f134600f0c397c8cc4cb8c3 6.2/en/os/sparc/krb5-libs-1.1.1-28.sparc.rpm
ffbedd3e39c838dbd844573df82c2c71 6.2/en/os/sparc/krb5-server-1.1.1-28.sparc.rpm
dfa66193f8a637d9ffe6c2e0ab37616a 6.2/en/os/sparc/krb5-workstation-1.1.1-28.sparc.rpm
4f6c71033da1c3b8a4b7755c0a02fc44 7.0/en/os/SRPMS/krb5-1.2.2-12.src.rpm
d8968499a52996909463f14fabb927ed 7.0/en/os/alpha/krb5-devel-1.2.2-12.alpha.rpm
d019c6e7b5e54a79f28fe4b8c70aa21a 7.0/en/os/alpha/krb5-libs-1.2.2-12.alpha.rpm
ec7240d34748981cedea7a71b9d6b945 7.0/en/os/alpha/krb5-server-1.2.2-12.alpha.rpm
0a83d1908ecb2ed8d6c60c7680c4ea9c 7.0/en/os/alpha/krb5-workstation-1.2.2-12.alpha.rpm
b9052937bdc499d739d966aed7dc6d78 7.0/en/os/i386/krb5-devel-1.2.2-12.i386.rpm
ddf2a15cfa2d35ecaab5c03a28ac1113 7.0/en/os/i386/krb5-libs-1.2.2-12.i386.rpm
87ff31faee86931f70aec8a271090756 7.0/en/os/i386/krb5-server-1.2.2-12.i386.rpm
9c5341e2479f0641adb5ecadd2c3d5ac 7.0/en/os/i386/krb5-workstation-1.2.2-12.i386.rpm
4f6c71033da1c3b8a4b7755c0a02fc44 7.1/en/os/SRPMS/krb5-1.2.2-12.src.rpm
d8968499a52996909463f14fabb927ed 7.1/en/os/alpha/krb5-devel-1.2.2-12.alpha.rpm
d019c6e7b5e54a79f28fe4b8c70aa21a 7.1/en/os/alpha/krb5-libs-1.2.2-12.alpha.rpm
ec7240d34748981cedea7a71b9d6b945 7.1/en/os/alpha/krb5-server-1.2.2-12.alpha.rpm
0a83d1908ecb2ed8d6c60c7680c4ea9c 7.1/en/os/alpha/krb5-workstation-1.2.2-12.alpha.rpm
b9052937bdc499d739d966aed7dc6d78 7.1/en/os/i386/krb5-devel-1.2.2-12.i386.rpm
ddf2a15cfa2d35ecaab5c03a28ac1113 7.1/en/os/i386/krb5-libs-1.2.2-12.i386.rpm
87ff31faee86931f70aec8a271090756 7.1/en/os/i386/krb5-server-1.2.2-12.i386.rpm
9c5341e2479f0641adb5ecadd2c3d5ac 7.1/en/os/i386/krb5-workstation-1.2.2-12.i386.rpm
7ec4e94edb5d39ce08b847601920975b 7.1/en/os/ia64/krb5-devel-1.2.2-12.ia64.rpm
31fbb239efc795864bfb5f2d01278c5f 7.1/en/os/ia64/krb5-libs-1.2.2-12.ia64.rpm
35f3d405ace519cf983b4f584c3f30de 7.1/en/os/ia64/krb5-server-1.2.2-12.ia64.rpm
91721e2dc00c05b1f9183182f64ad7f7 7.1/en/os/ia64/krb5-workstation-1.2.2-12.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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