Public Vulnerability Reports

AOL Instant Messenger aim:goaway URI Handler Buffer Overflow Vulnerability



AOL Instant Messenger is an instant messaging client developed by
America Online.


Remote exploitation of a buffer overflow vulnerability in America Online
Inc.'s Instant Messenger (AIM) can allow attackers to execute arbitrary

The vulnerability specifically exists due to insufficient bounds
checking on user-supplied values passed to the 'goaway' function of the
AOL Instant Messenger 'aim:' URI handler. A long message buffer will
overwrite values stored on the stack and may be used to overwrite a
Structured Exception Handler (SEH) pointer as shown below:

0012E634 45454545
0012E638 46464646
0012E63C 47474747
0012E640 484808EB Pointer to next SEH record
0012E644 41414141 SE handler

Control of the SEH pointer allows for eventual execution of arbitrary


Exploitation allows remote attackers to execute arbitrary code under the
privileges of the user that instantiated the vulnerable version of AOL
Instant Messenger. While AIM 5.5 and later has been compiled with
Microsoft Visual Studio .NET 2003 and incorporates stack protection,
iDEFENSE has confirmed that exploitation is still possible.


iDEFENSE has confirmed that AOL Instant Messenger, version 5.5, is
vulnerable. Previous versions are also suspected as vulnerable.


Exploitation of 'aim:' URI handler vulnerabilities can be prevented by
removing the following key from the registry:


The following script can be saved to a file with the .vbs extension and
executed to automate the task of removing the relevant URI handler:

Set WshShell = CreateObject("WScript.Shell")
WshShell.RegDelete "HKCRaim"

The AIM client will restore the HKEY_CLASSES_ROOTaim registry keys
upon initial execution provided that the user starting the application has
the appropriate registry permissions. In such cases, the workaround is
effective for only one session and must be re-applied upon the start of
a new session.


iDEFENSE has been working with AOL since 07/12/2004 regarding this issue
to allow the vendor time to implement a patch. However, on 08/09/2004 an
advisory was released by Secunia (
as the same issue was discovered by another group of researchers. With
the issue is now public, iDEFENSE is proceeding with public disclosure.
AOL has provided the following statement:

"iDEFENSE, Inc. reported a buffer overflow vulnerability in all Windows
versions of AOL Instant Messenger (AIM).  The impact of this
vulnerability could potentially allow for an attacker to execute
malicious code on Windows platforms.  Exploit of this vulnerability
requires that an AIM user click on a malicious URL supplied in an
instant message or embedded in a web page.

Affected Products and Applications

AOL Instant Messenger (AIM) for Windows - All known versions

Vendor Recommendations

1. America Online, Inc. recommends that Windows users of AIM upgrade to
the latest beta version to be released on August 9, 2004. This new
version of AIM addresses the vulnerability described herein and can be
obtained via the AOL Instant Messenger portal,

2. A workaround provided by iDEFENSE is available until users are able
to upgrade to the new beta version.

3. The code fixes to AIM 5.5 to resolve the recent URL:goaway vulnerability
will be included in the next release of International versions due August 25.

Vendor Acknowledgments

Thanks to Matt Murphy and iDEFENSE, Inc. for their assistance to
responsibly address this issue."


The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2004-0636 to this issue. This is a candidate for inclusion in
the CVE list (, which standardizes names for
security problems.


06/16/2004    Initial vendor contact
06/16/2004    iDEFENSE clients notified
07/07/2004    Secondary vendor contact
07/12/2004    Initial vendor response
08/09/2004    Coordinated public disclosure


Matt Murphy is credited with this discovery.

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Copyright © 2004 Verisign, Inc.

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at the time of publishing based on currently available information. Use
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