What Enterprise Security Teams Need to Know About Client-Side Attacks

As businesses continue to expand their digital presences, addressing and managing client-side attack vulnerabilities has become more crucial than ever.

Client-side attacks represent a critical threat vector that targets code and data executed or stored on the user's browser rather than on the server.

These attacks exploit vulnerabilities within the client-side environment of web applications — everything from the HTML and JavaScript that run in the user's browser to client-side storage mechanisms. This type of attack can lead to unauthorized access to personal data, session hijackings, and other malicious activities that compromise both the user and the integrity of the website.

The bad news is that the prevalence of client-side attacks has seen a significant rise, driven by the increasing complexity of web applications and their reliance on numerous third-party scripts and services. This escalation not only amplifies potential entry points for attackers but also poses substantial risks to enterprise security. The impact of these attacks on businesses can be profound, ranging from direct financial losses due to fraud, reputational damage affecting customer trust, and potential regulatory penalties for failing to safeguard user data.

So, as enterprises continue to expand their digital footprints, the urgency to address and mitigate client-side vulnerabilities has never been more critical. In this post, let’s dive deeper into these attacks and what you can do to prevent them.

Understanding Client-Side Attacks

As mentioned earlier, client-side attacks occur within the user's browser, manipulating web pages through the code executed on the client side, like JavaScript or HTML. This is in stark contrast to server-side attacks, which target the server's infrastructure and resources directly.

The distinction lies in the attack surface: client-side attacks exploit the vulnerabilities present in the user’s local environment (such as the web browser), while server-side attacks focus on compromising the backend infrastructure, such as databases and application servers.

Here are some common types of client-side attacks.

• Formjacking: This attack involves cybercriminals injecting malicious JavaScript code into online forms on websites to steal sensitive information provided by users, like credit card details and login credentials. This stolen data is then often sold on the dark web or used for further fraudulent activities.
• Cross-Site Scripting (XSS): XSS attacks inject malicious scripts into web pages viewed by other users. These scripts can hijack user sessions, deface web sites, or redirect the user to malicious sites. Unlike other attacks, XSS exploits the trust a user has for a particular site, turning it against them.
• Magecart Attacks: Specifically targeting e-commerce sites (even those that are PCI DSS 4.0 compliant), Magecart attacks involve hackers injecting malicious scripts into the website to skim credit card details when transactions are made. This type of attack exploits third-party services integrated into websites, such as payment gateways, to intercept data during the transaction process.

Recent years have witnessed several high-profile client-side attacks. For instance, the attack on British Airways is a well-known example of a client-side attack, specifically a Magecart attack. In 2018, attackers compromised the airline's website by injecting malicious JavaScript into the payment page. This script captured payment card information, names, and addresses as customers entered them during the checkout process. The breach affected approximately 380,000 customers, and the data was silently harvested and transmitted to the attackers' servers.

This incident led to a significant fine for British Airways, initially set to be £183 million by the UK's Information Commissioner's Office (ICO) due to the severe nature of the data breach and non-compliance with the General Data Protection Regulation (GDPR). However, the fine was later reduced to £20 million. The British Airways breach underscores the critical importance of securing web applications and monitoring third-party scripts to protect user data from such sophisticated attacks.

Another example is The Simone Veil Hospital in Cannes, which suffered a cyberattack this past April that forced its staff to revert to pen and paper. It was later confirmed that the LockBit 3.0 ransomware group was attempting to extort the hospital. This incident highlights the vulnerability of healthcare providers to client-side attacks, which can severely disrupt operations and patient care.

Vulnerabilities and Entry Points

Enterprise web applications are complex systems that often integrate numerous external resources and scripts, which can introduce vulnerabilities exploitable by attackers. Understanding these vulnerabilities and their entry points is crucial for enhancing security and mitigating risks.

The two most common vulnerabilities exploited by attackers are third-party JavaScript and unsecured form submissions.

Use of Third-Party JavaScript

One of the most significant vulnerabilities comes from the use of third-party JavaScript. Many modern websites rely on external scripts for a variety of functions, including user interfaces, analytics and ads. While these scripts provide valuable services, they also create potential entry points for attackers. 

If a third-party service is compromised, malicious scripts can be injected into every website that uses that service. This is particularly dangerous, because it allows attackers to execute scripts directly in the user’s browser, often without the website owner’s knowledge.

For example, the Magecart attack groups exploit these vulnerabilities by injecting skimming scripts into third-party components to steal data directly from the user's browser. This approach was notably used in the attacks on British Airways, where attackers compromised the airline's website to capture customer data during transactions.

Insecure Form Submissions

Insecure form submissions are another common vulnerability that attackers exploit. Many websites collect information via forms, such as login credentials, personal information, and payment details. If these forms are not properly secured, attackers can intercept the data submitted by users. This can be done through various techniques, such as formjacking and XSS.

Furthermore, the role of third-party code in web applications highlights a broader issue of supply chain weaknesses. The integration of external services and scripts into web applications creates a supply chain that can be exploited by attackers. A single vulnerability in any part of this chain can compromise the security of the entire application. This was vividly illustrated in the SolarWinds attack, where malicious code was inserted into the software's build environment, affecting thousands of clients downstream.

Supply chain attacks can be particularly challenging to defend against because they exploit the interconnectedness and dependencies of modern software development. Organizations must vet third-party providers rigorously and implement strict security controls for any third-party code integrated into their systems.

Preventive Measures and Best Practices

Safeguarding enterprise web applications from client-side attacks necessitates employing a combination of preventive approaches and robust security technologies, including the following.

• Content Security Policy (CSP): CSP is an effective security standard that helps prevent cross-site scripting (XSS), clickjacking, and other code injection attacks originating from malicious content. By specifying which domains, a browser should consider valid sources of executable scripts and styles, CSP serves as an allowlist, prohibiting the browser from loading any unauthorized external resources that could harbor malicious intent.
• Subresource Integrity (SRI): SRI is a security feature that enables browsers to verify that the resources they fetch (such as scripts or stylesheets) are delivered without unexpected manipulation. It works by allowing you to provide a cryptographic hash that a fetched resource must match. This is particularly useful for ensuring the integrity of resources served by third-party CDNs that might be compromised.

Here are some best practices to secure client-side applications.

Regular Audits of Third-Party Scripts

Continuously monitor and audit all third-party scripts used on your site. This involves checking for updates, verifying their sources, and understanding what data they access. Regular audits help in identifying any anomalies or unauthorized changes that could indicate a compromise.

Implementation of Sandboxing Techniques

Sandboxing isolates a web application from the rest of the system. Any malicious code found within the app is confined to the sandbox, minimizing the risk to the overall system. This technique is particularly effective in mitigating the effects of a successful attack.

Using a Layered Security Approach

Implement multiple layers of security controls throughout the application to reduce the risk of client-side attacks. This approach, often referred to as "defense in depth," ensures that even if one security layer fails, additional layers provide continued protection.

Adopting the Right Tools

This includes Web Application Firewalls (WAFs) that help protect web applications by filtering and monitoring HTTP traffic between a web application and the Internet. They help defend against XSS, SQL injection, and other known threats by inspecting incoming traffic and blocking malicious requests.

Also, use secure application frameworks that are designed with security in mind, which can automatically handle many client-side security issues such as XSS and CSRF (Cross-Site Request Forgery) protections. Frameworks like Angular and React, for instance, provide automatic escape from output, which helps prevent XSS attacks.

Wrapping Up

The sophistication and impact of client-side attacks, as seen in the high-profile breaches discussed, demonstrates the critical gaps in many organizations' current security postures.

To safeguard sensitive data and maintain customer trust, businesses need to implement proactive and preventive security measures. This includes adopting technologies such as Content Security Policies (CSP) and Subresource Integrity (SRI), conducting regular audits of third-party scripts, and employing a layered security approach that includes the use of Web Application Firewalls (WAFs) and secure application frameworks.

The time to strengthen client-side defenses is now — before attackers exploit vulnerabilities that could lead to the next big data breach.