IBM AIX ftp gets() Multiple Buffer Overflow Vulnerabilities

iDefense Security Advisory 07.26.07
http://labs.idefense.com/intelligence/vulnerabilities/
Jul 26, 2007

I. BACKGROUND

The ftp program is a client application for accessing data stored on FTP
servers. This client is responsible for interfacing with users and
speaking the FTP protocol with remote servers. Under AIX, the ftp
program is installed by default and is setuid root. More information
can be found at the following URL.

http://publib.boulder.ibm.com/infocenter/pseries/v5r3/topic/com.ibm.aix.cmds/doc/aixcmds2/ftp.htm

II. DESCRIPTION

Local exploitation of multiple buffer overflow vulnerabilities in the
'ftp' program, as included with IBM Corp.'s AIX operating system, allow
an attacker to execute arbitrary code with root privileges.

These vulnerabilities exist due to several calls to the gets() function.
The gets() function is a deprecated C library function used to read data
from standard input into a buffer. This function provides no way to
specify the maximum size of the buffer being read into, and therefore
allows the buffer to be overflowed.

III. ANALYSIS

Exploitation of any of these vulnerabilities results in the execution of
arbitrary code with root privileges.

The ftp program is setuid root, and executable by any user with local
access. At least one of these vulnerabilities results in a trivially
exploitable stack-based buffer overflow.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in AIX
version 5.3 with service pack 6. Previous versions may also be
affected.

V. WORKAROUND

Removing the setuid bit from the binary will prevent exploitation, but
may make the program unusable by non-root users.

VI. VENDOR RESPONSE

IBM Corp. has addressed this vulnerability by releasing interim fixes.
More information can be found via the Bulletins tab of IBM's
Subscription Service for UNIX and Linux servers. You can reach this
service by clicking the URL shown below.

http://www14.software.ibm.com/webapp/set2/subscriptions/pqvcmjd?mode=1

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-4004 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

06/05/2007  Initial vendor notification
06/08/2007  Initial vendor response
07/26/2007  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
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