Software Engineering Institute

The Citrix Presentation Server Client software provides an ActiveX control that can be used to integrate the client into Web pages. The Citrix ICA Client ActiveX control, which is provided by Wfica.ocx, contains a buffer overflow vulnerability in the SendChannelData() method.

Citrix notes that his vulnerability is present in all versions of the Citrix Presentation Server Client for Windows earlier than 9.230.

By convincing a user to view a specially crafted HTML document (e.g., a web page or an HTML email message or attachment), a remote, unauthenticated attacker may be able to execute arbitrary code with the privileges of the user. The attacker could also cause Internet Explorer (or the program using the WebBrowser control) to crash.

Upgrade

Citrix has provided updated versions of the affected software to address this issue. Please see the corresponding Citrix Security Bulletin for more information.

Disable the affected ActiveX control in Internet Explorer

The Citrix Presentation Server Client ActiveX control can be disabled in Internet Explorer by setting the kill bit for the following CLSID:

{238F6F83-B8B4-11CF-8771-00A024541EE3}
More information about how to set the kill bit is available in Microsoft Support Document 240797. Alternatively, the following text can be saved as a .REG file and imported to set the kill bit for this control:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{238F6F83-B8B4-11CF-8771-00A024541EE3}]
"Compatibility Flags"=dword:00000400
Disable ActiveX

Disabling ActiveX controls in the Internet Zone (or any zone used by an attacker) appears to prevent exploitation of this and other ActiveX vulnerabilities. Instructions for disabling ActiveX in the Internet Zone can be found in the "Securing Your Web Browser" document.