Description of Problem
A vulnerability has been identified in the Citrix Online Plug-ins and ICA Clients for XenApp and XenDesktop that could allow an attacker to impersonate an SSL or TLS endpoint. Customers should be aware that this issue is unrelated to the TLS renegotiation prefix injection attack, referenced by CVE-2009-3555.
SSL/TLS can be used to provide server authentication for ICA traffic in XenDesktop or XenApp. This vulnerability could allow an attacker to use a specifically crafted certificate to successfully impersonate the SSL/TLS server, in effect allowing the attacker to subvert the intended server authentication.
In addition to the specific issues documented in this bulletin, customers are strongly advised to follow the guidance in Microsoft security bulletin MS09-056, because some Citrix client components have dependencies on the components covered by this bulletin.
This issue has been resolved in the following clients:
• Citrix Online Plug-in for Windows: version 11.0.150, and version 11.2 and later
• Citrix Online Plug-in for Mac: version 11.0 and later
• Citrix Receiver for iPhone: version 1.0.3 and later
Customers are strongly advised to deploy the latest versions of these clients, available from the following location:
In order to exploit this issue, an attacker would need to obtain a specifically crafted certificate from a trusted certificate authority (CA). Certificate authorities could detect attempts to obtain such a certificate and refuse to issue it. In addition to obtaining such a certificate, an attacker would have to set up an SSL/TLS server and cause a legitimate client to connect to it.
What Citrix Is Doing
Obtaining Support on This Issue
If you require technical assistance with this issue, please contact Citrix Technical Support. Contact details for Citrix Technical Support are available at http://www.citrix.com/site/ss/supportContacts.asp
Customers should note that security updates are only released for currently supported clients. Legacy clients are listed on the Citrix download page, in the “Legacy Clients” category; more information about the support policy for these clients can be found on the Citrix website at the following location:
Reporting Security Vulnerabilities to Citrix
Citrix welcomes input regarding the security of its products and considers any and all potential vulnerabilities seriously. If you would like to report a security issue to Citrix, please compose an e-mail to firstname.lastname@example.org stating the exact version of the product in which the vulnerability was found and the steps needed to reproduce the vulnerability.