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A user makes some REST API calls to a server and the responses from the server include third-party executable code. The user notices that the responses do not work. Which network device may prevent the third-party code from execution?

• firewall
• Layer 3 switch
• proxy server
• reverse proxy server

A firewall is a network security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules. Firewalls are crucial in protecting networks from unauthorized access, cyberattacks, and malware. Here’s how a firewall can prevent third-party executable code from executing:

1. Traffic Filtering:
   • Firewalls can filter traffic based on a variety of criteria, including IP addresses, port numbers, protocols, and content types. By doing so, they can block traffic that contains executable code or scripts.
2. Intrusion Prevention Systems (IPS):
   • Many modern firewalls include integrated IPS, which can detect and block malicious activities, including the transmission of malicious code. IPS can analyze network traffic in real-time and prevent the execution of suspicious or known malicious executables.
3. Application Layer Gateways:
   • Firewalls with application layer gateways (ALGs) can inspect and filter traffic at the application level. This includes the ability to scrutinize the content of HTTP responses and block any executable code that violates security policies.
4. Deep Packet Inspection (DPI):
   • DPI allows firewalls to examine the data part (and possibly the header) of a packet as it passes an inspection point. Firewalls with DPI capabilities can detect and prevent malicious code embedded in API responses from reaching the end user.
5. URL Filtering:
   • Firewalls can block requests to known malicious domains or URLs. If the third-party code is hosted on such domains, the firewall can prevent the user from accessing it, thereby stopping the execution of the code.
6. Sandboxing:
   • Some advanced firewalls have sandboxing capabilities where suspicious files or code are executed in a controlled environment to observe their behavior before allowing them through. This can prevent harmful executables from reaching the user.

Practical Scenario

• When a user makes REST API calls, the firewall can be configured to inspect the responses. If the responses contain executable code that matches known malware signatures or violates predefined security policies, the firewall can block this traffic.
• For example, a firewall might be set to block all executables (.exe files), scripts (.js files), or other types of code from being downloaded. When the API response includes such a file, the firewall intercepts and blocks it.

Comparison with Other Devices

• Layer 3 Switch:
  • Primarily routes traffic within a network and does not inspect or block content at the application layer.
• Proxy Server:
  • Acts as an intermediary and can filter content, but its primary role is to cache, anonymize, and control access rather than specifically block executable code.
• Reverse Proxy Server:
  • Primarily protects the server from client requests, providing load balancing and caching, rather than blocking executable code in responses.

Conclusion

A firewall, especially one with advanced security features like IPS, DPI, and application layer filtering, is well-equipped to prevent the execution of third-party executable code by blocking or inspecting harmful responses from REST API calls.