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CA-2001-34 Buffer Overflow in System V Derived Login


CERT Advisory CA-2001-34 Buffer Overflow in System V Derived Login

Original release date: December 12, 2001
Last revised: --
Source: CERT/CC

A complete revision history can be found at the end of this file.

Systems Affected

* IBM AIX versions 4.3 and 5.1
* Hewlett-Packard's HP-UX
* SCO OpenServer 5.0.6 and earlier
* SGI IRIX 3.x
* Sun Solaris 8 and earlier


Several applications use login for authentication to the system. A
remotely exploitable buffer overflow exists in login derived from
System V. Attackers can exploit this vulnerability to gain root access
to the server.

I. Description

Several implementations of login that are derived from System V allow
a user to specify arguments such as environment variables to the
process. An array of buffers is used to store these arguments. A flaw
exists in the checking of the number of arguments accepted. This flaw
permits the array of buffers to be overflowed.

On most systems, login is not suid; therefore, it runs as the user who
called it. If, however, login is called by an application that runs
with greater privileges than those of the user, such as telnetd or
rlogind, then the user can exploit this vulnerability to gain the
privileges of that program. In the case of telnetd or rlogind, root
access is gained.

Since in.telnetd and in.rlogind are available over the network, a
remote attacker without any previous access to the system could use
this vulnerability to gain root access to the system.

If a program that invokes login is suid (or sgid) USER_A, then this
can be exploited to gain the privileges of USER_A.

An exploit exists and may be circulating.

II. Impact

This vulnerability can be remotely exploited to gain privileges of the
invoker of login. In the case of a program such as telnetd, rlogind,
or other suid root programs, root access is gained.

III. Solution

Apply a patch from your vendor

Appendix A contains information provided by vendors for this advisory.
As vendors report new information to the CERT/CC, we will update this
section and note the changes in our revision history. If a particular
vendor is not listed below, we have not received their comments.
Please review the VU#569272 for your vendor's status or contact your
vendor directly.

Restrict access to login

We recommend disabling TELNET, RLOGIN and other programs that use
login for authentication. Do not use programs that use a vulnerable
login for authentication. Note that some SSH applications can be
configured to use login for authentication. If this configuration is
selected, then you will still be vulnerable.

If you cannot disable the service, you can limit your exposure to
these vulnerabilities by using a router or firewall to restrict access
to port 23/TCP (telnet) and port 513/TCP (rlogin). Note that this does
not protect you against attackers from within your network.

Appendix A. - Vendor Information

This appendix contains information provided by vendors for this
advisory. As vendors report new information to the CERT/CC, we will
update this section and note the changes in our revision history. If a
particular vendor is not listed below, we have not received their

Apple Computer, Inc.

Mac OS X and Mac OS X Server are not vulnerable.


We are not using a SystemV based /bin/login, we are using the BSD
originated rlogin tools. All OpenLinux products are 'Not Vulnerable'.

Compaq Computer Corporation

Compaq's Tru64 Software is not impacted by this reported problem.

Cray Inc.

Cray Inc. has determined that its implementation of login is not
vulnerable to the situation described in VU#569272.


HP-UX is NOT Exploitable, even though HP-UX does have the buffer
overflow, and hence is listed as "effected" above. In any case, the
buffer overflow has been fixed by HP.


IBM's AIX operating system, versions 4.3 and 5.1, are susceptible to
this vulnerability. We have prepared an emergency fix ("efix"),
"tsmlogin_efix.tar.Z", and it is available for downloading from:

The APAR assignment for AIX 5.1 is IY26221, and will be available
soon. The APAR for AIX 4.3 is pending, as a new level of 4.3 is nearly
available. The "README" file at the above FTP site will be updated to
provide the official fix information and availability.


NetBSD does not use a System V derived login, and therefore, NetBSD is
not vulnerable.

Red Hat

Red Hat Linux does not use a System V derived /bin/login, and is
therefore not vulnerable to this.

Sun Microsystems

Sun has developed a fix and T-patches are being tested. Official
patches will be released shortly and Sun will issue a Sun Security
Bulletin when they are available.

The CERT Coordination Center thanks Internet Security Systems and Sun
Microsystems for the technical information they provided.

Feedback on this document can be directed to the author,
Jason A. Rafail


This document is available from:

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Copyright 2001 Carnegie Mellon University.

Revision History
December 12, 2001 : Initial Release

Version: PGP 6.5.8


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