T1203 - Exploitation for Client Execution

Adversaries may exploit software vulnerabilities in client applications to execute code. Vulnerabilities can exist in software due to unsecure coding practices that can lead to unanticipated behavior. Adversaries can take advantage of certain vulnerabilities through targeted exploitation for the purpose of arbitrary code execution. Oftentimes the most valuable exploits to an offensive toolkit are those that can be used to obtain code execution on a remote system because they can be used to gain access to that system. Users will expect to see files related to the applications they commonly used to do work, so they are a useful target for exploit research and development because of their high utility.

Several types exist:

Browser-based Exploitation

Web browsers are a common target through Drive-by Compromise and Spearphishing Link. Endpoint systems may be compromised through normal web browsing or from certain users being targeted by links in spearphishing emails to adversary controlled sites used to exploit the web browser. These often do not require an action by the user for the exploit to be executed.

Office Applications

Common office and productivity applications such as Microsoft Office are also targeted through Phishing. Malicious files will be transmitted directly as attachments or through links to download them. These require the user to open the document or file for the exploit to run.

Common Third-party Applications

Other applications that are commonly seen or are part of the software deployed in a target network may also be used for exploitation. Applications such as Adobe Reader and Flash, which are common in enterprise environments, have been routinely targeted by adversaries attempting to gain access to systems. Depending on the software and nature of the vulnerability, some may be exploited in the browser or require the user to open a file. For instance, some Flash exploits have been delivered as objects within Microsoft Office documents.

Atomic Tests:

Currently, no tests are available for this technique.

Detection

Detecting software exploitation may be difficult depending on the tools available. Also look for behavior on the endpoint system that might indicate successful compromise, such as abnormal behavior of the browser or Office processes. This could include suspicious files written to disk, evidence of Process Injection for attempts to hide execution, evidence of Discovery, or other unusual network traffic that may indicate additional tools transferred to the system.

Shield Active Defense

Decoy System

Configure a computing system to serve as an attack target or experimental environment.

A decoy system is a computing resource presented to the adversary in support of active defense. The underlying system can be real, virtual, or simulated, and can be presented as one of a variety of IT devices including user workstations, servers, networking systems, IOT (embedded devices), mobile systems like phones, etc.

Opportunity

There is an opportunity to study the adversary and collect first-hand observations about them and their tools.

Use Case

A defender can use a decoy system to see if an adversary exploits vulnerable software in order to compromise the system.

Procedures

Use an isolated system to visit a suspected compromised website. Collect any associated scripting code or files dropped onto the system. Setup a server which appears to be something that is commonly expected within a network, such as web server.