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Client Application Security

Client-side application security covers the risks introduced when software on an end-user machine communicates with external servers, and the controls needed to address those risks.

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About this video

Client-side application security addresses the risks that arise when software installed on an end-user machine communicates with external servers. Modern applications rarely operate in isolation — most connect to remote servers at minimum to retrieve updates, and many depend on those servers for core functionality. This client-server relationship, while essential to how contemporary software works, expands the attack surface and introduces vulnerabilities that must be actively managed. Web browsers represent a particularly significant risk because they connect to a wide range of servers, many of which may be unknown or untrusted from a security standpoint. Controlling which applications are permitted on a machine is a foundational countermeasure, with the principle that unnecessary applications should not be installed at all. When an application must be present, it should be configured securely and monitored appropriately. Beyond application control, two additional attack vectors demand attention. DNS security ensures that when users navigate to a domain name, they are resolved to the correct server and not redirected to a malicious one. Email security addresses the risk of malicious code delivered through incoming messages, requiring measures that detect and block viruses and malware before they can execute on the endpoint. Together, these controls form the foundation of a client-side security posture.

What you'll learn

Identify common client-side application security risks, including threats associated with web browsers, DNS resolution, and email clients
Explain the client-server model and how externally connected applications introduce security vulnerabilities on endpoint systems

What's covered

Client-Side Application Security

Applications Overview
- Software on a Computer
  - Word Processors
  - Spreadsheets
  - Web Browsers
- Security Concerns
Client-Server Relationship
- Client Requests Service
- Server Hosts Web Pages
- Web Browser Communication
Application Control
- Control Installed Apps
- Monitor Web Browsers
- Secure App Configuration
Key Attack Vectors
- DNS Security
  - Wrong DNS Information
  - Connecting to Wrong Server
- Email Security
  - Malicious Code in Emails
  - Viruses and Malware

Key terms

Server: A computer or program that provides services or resources to other devices, known as clients, over a network.
Endpoint: Any device that connects to a network, including computers, smartphones, tablets, and IoT devices.
Domain Name System: A hierarchical naming system that translates human-readable domain names into IP addresses.
DNS Poisoning: An attack that corrupts the DNS cache to redirect users to malicious websites.
Phishing: A social engineering attack that uses deceptive emails or messages to trick users into revealing sensitive information.
Malware: Software specifically designed to disrupt, damage, or gain unauthorized access to a system.
Vulnerability: A weakness in a system, application, or process that can be exploited by a threat actor.
Client-Server Model: A computing architecture in which a client device requests services or resources from a remote server over a network.
Web Browser: A client application that retrieves web pages from servers using HTTP or HTTPS, interprets HTML, CSS, and JavaScript, and renders the results as an interactive visual display for the user.
Application Control: A security mechanism that restricts which applications are permitted to execute on a system, typically using allowlists or blocklists. Application control prevents unauthorized or malicious software from running even if it reaches the endpoint.

Topics

Client Side Security Web Browser Security Dns Security Email Security Client Server Model Endpoint Security Cybersecurity

Transcript

What an application is

An application is just software, software that's running on a computer, and it's software that is helping us perform certain tasks. So for instance, if I am typing up a paper, then I have a word processor application. Or if I'm typing up a spreadsheet, then I have a spreadsheet application. Maybe I'm connecting to the web: well, now I have some sort of web browsing application, which we call a browser. So this is an app on the machine.

By installing these apps, we can introduce some security concerns, especially if these apps are connecting to some sort of external server. In fact, a lot of our apps, maybe even most of our apps nowadays, are connecting to some sort of external server. At the very least, they're getting updates, to check to see if they need to patch or update this application right here. But in a lot of cases, they're actually getting a lot of their services, a lot of their functionality, from communicating to a server.

The client-server relationship

So what does this client server relationship look like? We have a client right here, and it connects to a server. A client is just the machine that needs some sort of service. The server is hosting that service.

Right here we have a service that's running. This specific example of a service is www services, or we call this a web server. So this is a web server right here that's hosting out web pages. This client has an application on it. This application allows us to view the web pages that this web server is sending us. So this application requests certain information, the web server then returns that information, and it's displayed in this application. We call this a web browser.

Application control

Because there are some significant security holes that can happen on these applications, we need to practice some sort of application control. That is, controlling what applications actually get installed on these machines, making sure that there's no applications that shouldn't be installed on the machine.

And we especially have to be concerned around web browsers, things like Chrome or Safari or Firefox. These applications are reaching out and connecting to the outside world, many times to servers that we've never visited before, that are unknown from a security perspective, and we need to be concerned about that.

So we need to protect this client machine. We need to protect the end user. We need to protect the communication that's going between these servers, and make sure that we're connecting to the right servers.

DNS and email

We're not typically typing in an IP address to get to these servers. Instead, what we're doing is we're typing some sort of domain name and host in there, and then getting to this server so that way we can retrieve information. Well, if we get the wrong DNS information, we're going to go to the wrong server. So we also need to be concerned about DNS security and how we're resolving these names.

Another big attack vector is emails. When we get emails on our machine, it can have malicious code inside that email. So how do we protect the email that comes into our system and make sure that it doesn't have any kind of viruses or malware that are installed on it? So we need to make sure we consider email security with this as well.

Ultimately the best practice is not to have this application at all, so we want to practice some sort of application control. But if we must have it, then we need to make sure that the application is secure in the way that it's set up.

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