Pierluigi Paganini May 02, 2019

A flaw in Dell SupportAssist, a pre-installed tool on most Dell computers, could be exploited by hackers to compromise them remotely.

The security researcher Bill Demirkapi (17) has discovered a critical remote code execution vulnerability in the Dell SupportAssist utility that is pre-installed on most Dell computers.

The vulnerability could be exploited by hackers to compromise systems remotely.

Dell SupportAssist software is described as a tool that proactively checks the health of system’s hardware and software. When an issue is detected, the necessary system state information is sent to Dell for troubleshooting.

To solve the problems Dell SupportAssist interacts with the Dell Support website and automatically detect Service Tag or Express Service Code of Dell product.

The utility performs hardware diagnostic tests and analyzes the hardware configuration of the system, including installed device drivers, and is able to install missing or available driver updates.

The software leverages a local web service that is protected using the “Access-Control-Allow-Origin” response header and implementing restrictions to accept commands only from the “dell.com” website or its subdomains,

“On start, Dell SupportAssist starts a web server (System.Net.HttpListener) on either port 8884, 8883, 8886, or port 8885. The port depends on whichever one is available, starting with 8884. On a request, the ListenerCallback located in HttpListenerServiceFacade calls ClientServiceHandler.ProcessRequest. ClientServiceHandler.ProcessRequest, the base web server function, starts by doing integrity checks for example making sure the request came from the local machine and various other checks” reads the analysis published by Bill Demirkapi.

“An important integrity check for us is in ClientServiceHandler.ProcessRequest, specifically the point at which the server checks to make sure my referrer is from Dell.”

Demirkapi discovered that it is possible to bypass the protections implemented by Dell and download and execute malicious code from a remote server under the control of the attackers.

“To bypass the Referer/Origin check, we have a few options:

1. Find a Cross Site Scripting vulnerability in any of Dell’s websites (I should only have to find one on the sites designated for SupportAssist)
2. Find a Subdomain Takeover vulnerability
3. Make the request from a local program
4. Generate a random subdomain name and use an external machine to DNS Hijack the victim. Then, when the victim requests [random].dell.com, we respond with our server.”

Dell acknowledged the flaw as explained in a security advisory and released a security update to address it:

“An unauthenticated attacker, sharing the network access layer with the vulnerable system, can compromise the vulnerable system by tricking a victim user into downloading and executing arbitrary executables via SupportAssist client from attacker hosted sites,” reads the advisory.

The remote code execution flaw, tracked as CVE-2019-3719, affects Dell SupportAssist Client versions prior to version 3.2.0.90.

The expert published a video PoC of the hack and the source code of the proof of concept:

Pierluigi Paganini

(SecurityAffairs – Dell SupportAssist, hacking)

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