Denial of Service in Citrix MetaFrame

Reported October 16, 2001, byInternet Security Systems.

VERSIONS AFFECTED

DESCRIPTION
Avulnerability exists in the Citrix MetaFrame server application that lets anattacker crash the server, resulting in a Denial of Service (DoS). An improperhandling of multiple sessions on the Citrix servercauses this DoS condition. By spoofing the protocol thatruns between the MetaFrame client and server, an attacker can start multiplefake sessions with the affected server. These sessions typically pass filenameand other information from client to server before the system has set upencrypted channels. The server lets an attacker start a maximum of approximately52 sessions. After these sessions time out, any new sessions that start cancause the server to crash with a blue screen.

VENDOR RESPONSE

Thevendor, Citrix, recommends that usersinstall the appropriate hotfixesthat the vendor will make available soon.

CREDIT
Discovered by Justine Bone, Glyn Geoghegan, and Paul Davies of InternetSecurity Systems.