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SunOS : Buffer Overflow in /bin/login]

Internet Security Systems Security Advisory
December 12, 2001

Buffer Overflow in /bin/login


ISS X-Force has discovered a serious vulnerability in the "login"
program present in Sun Solaris systems. Login allows users to sign on to
the system by entering a username and password. This vulnerability
allows remote attackers to execute arbitrary commands on a target system
with superuser privilege. Systems are vulnerable to this issue only if
certain types of interactive connections are allowed, such as Telnet or
Rlogin. These services are enabled by default on most platforms. X-Force
has learned that an exploit for this vulnerability has been made public.

Affected Versions:

Sun Microsystems Solaris 8 and earlier

* Note: Additional SysV derived Unix operating systems may or may not be


A static buffer overflow vulnerability is present in the Sun Solaris
implementation of "login", otherwise known as "/bin/login" for its
location in the file system. Login is executed to authenticate remote
users as they initiate clear-text terminal connections over a network.
These types of connections are ubiquitous in modern networked

Login incorrectly handles long environment variables passed to it by
in.telnetd, in.rlogind, or any other similar daemon that operates in
conjunction with login. No local account or special knowledge of the
target is needed to successfully exploit this vulnerability.

There are secure alternatives to using Telnet and Rlogin that are not
vulnerable to this issue. Secure Shell (SSH) implements encrypted
terminal connections, and it is designed to replace insecure protocols
like Telnet and Rlogin. Recent versions of SSH implement their own
version of the login program, and are not vulnerable. However, some
versions of SSH may be configured to interact with login, and may be
vulnerable in this configuration.


There is no simple workaround for this issue. However, disabling all
default terminal communications services and installing SSH will
eliminate the vulnerability.

ISS X-Force urges that all vulnerable machines are patched as soon as
the vendor releases these updates. This advisory is being released
before patches are available, because the exploit for this vulnerability
has been made public.

Sun Microsystems, Inc.
Sun has reproduced the vulnerability and is testing a fix. Sun T-patches
are now available for this vulnerability. Official patches will soon be
available at the following location:

ISS RealSecure Network Sensor customers are currently protected from
this vulnerability. Support for this issue was included in X-Press
Update version 3.3 as the "TelnetExcessiveTabs" signature. This
signature will be included in the next RealSecure Server Sensor.

ISS Internet Scanner X-Press Update 6.1 for Internet Scanner version
6.2.1 included support for this issue with the TelnetTabBO check.

ISS BlackICE customers are protected from this vulnerability by the
"2000902 Telnet login name overflow" signature.

Additional Information:

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2001-0797 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

ISS X-Force Database,

CERT Vulnerabilty note,

CERT Advisory,


This vulnerability was discovered and researched by Mark Dowd of the ISS
X-Force. Internet Security Systems would like to thank Sun Microsystems
and CERT for their prompt response and handling of this vulnerability.


About Internet Security Systems (ISS)
Internet Security Systems is a leading global provider of security
management solutions for the Internet, protecting digital assets and
ensuring safe and uninterrupted e-business. With its industry-leading
intrusion detection and vulnerability assessment, remote managed
security services, and strategic consulting and education offerings, ISS
is a trusted security provider to more than 9,000 customers worldwide
including 21 of the 25 largest U.S. commercial banks, the top 10 U.S.
telecommunications companies, and all major branches of the U.S. Federal
Government. Founded in 1994, ISS is headquartered in Atlanta, GA, with
additional offices throughout North America and international operations
in Asia, Australia, Europe, Latin America and the Middle East. For more
information, visit the Internet Security Systems web site at www.iss.net
or call 888-901-7477.

Copyright (c) 2001 Internet Security Systems, Inc. All rights reserved

Permission is hereby granted for the redistribution of this Alert
electronically. It is not to be edited in any way without express
consent of the X-Force. If you wish to reprint the whole or any part
of this Alert in any other medium excluding electronic medium, please
e-mail xforce@iss.net for permission.


The information within this paper may change without notice. Use of this
information constitutes acceptance for use in an AS IS condition. There
are NO warranties with regard to this information. In no event shall the
author be liable for any damages whatsoever arising out of or in
connection with the use or spread of this information. Any use of this
information is at the user's own risk.

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Please send suggestions, updates, and comments to: X-Force
xforce@iss.net of Internet Security Systems, Inc.