Microsoft Forefront Unified Access Gateway (CVE-2011-1895) HTTP Response Splitting Vulnerability

Description

Microsoft Forefront Unified Access Gateway is prone to an HTTP response-splitting vulnerability because it fails to sufficiently sanitize user-supplied data. Attackers can leverage this issue to influence or misrepresent how web content is served, cached, or interpreted. This could aid in conducting cross-site scripting attacks and various other attacks that try to entice client users into a false sense of trust.

Technologies Affected

• Microsoft Forefront Unified Access Gateway 2010
• Microsoft Forefront Unified Access Gateway 2010 SP1
• Microsoft Forefront Unified Access Gateway 2010 Update 1
• Microsoft Forefront Unified Access Gateway 2010 Update 2

Recommendations

Block external access at the network boundary, unless external parties require service.
Filter access to the affected computer at the network boundary if global access isn’t needed. Restricting access to only trusted computers and networks might greatly reduce the likelihood of a successful exploit.

Run all software as a nonprivileged user with minimal access rights.
Attackers may successfully exploit client flaws in the browser using this issue. When possible, run all software as a user with minimal privileges and limited access to system resources. Use additional precautions such as restrictive environments to insulate software that may potentially handle malicious content.

Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy NIDS to detect and block attacks and anomalous activity such as requests containing suspicious URI sequences. Since the webserver may log such requests, review its logs regularly.

Do not follow links provided by unknown or untrusted sources.
Web users should be cautious about following links to sites that are provided by unfamiliar or suspicious sources. Filtering HTML from emails may help remove a possible vector for transmitting malicious links to users.

Updates are available. Please see the references for more information.