IBM AIX ftp domacro Parameter Buffer Overflow Vulnerability

iDefense Security Advisory 10.30.07
http://labs.idefense.com/intelligence/vulnerabilities/
Oct 30, 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 set-uid root. More information
can be found at the URL shown below.

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

II. DESCRIPTION

Local exploitation of a buffer overflow vulnerability in the ftp client
of IBM Corp.'s AIX operating system allows attackers to execute
arbitrary code with root privileges.

The problem specifically exists within the domacro() function. This
function is called when executing a macro via the '$' command within
the ftp program. When executing a macro, the parameter is copied to a
fixed size stack buffer using an unbounded call to strcpy(). By
specifying a long argument, an attacker is able to overwrite program
control data located on the stack and take control of the affected
process.

III. ANALYSIS

Exploitation allows an attacker to execute arbitrary code with root
privileges. Local access is required to execute and interact with the
ftp program.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in AIX
version 5.3 (5300-06). Previous versions are suspected to be
vulnerable.

V. WORKAROUND

Removing the set-uid bit from the ftp program will protect against
exploitation. However, doing so will render the program unusable.

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-2007-4217 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

08/15/2007  Initial vendor notification
08/15/2007  Initial vendor response
10/30/2007  Coordinated public disclosure

IX. CREDIT

This vulnerability was discovered by Joshua J. Drake of VeriSign
iDefense Labs.

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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