Malicious Cyber Actors Exploiting Cross-Site Scripting Vulnerabilities: How to Protect Your Systems

Malicious Cyber Actors Exploiting Cross-Site Scripting Vulnerabilities: How to Protect Your Systems

The Cybersecurity and Infrastructure Security Agency (CISA) and the FBI have issued a Secure by Design Alert, highlighting the ongoing exploitation of cross-site scripting (XSS) vulnerabilities by malicious actors. Despite being a known threat, XSS vulnerabilities remain prevalent in software systems, giving attackers the opportunity to inject malicious scripts into web applications, leading to data theft and manipulation. However, XSS vulnerabilities are preventable, and software developers must prioritize building secure systems from the ground up.

What Causes XSS Vulnerabilities?

Cross-site scripting vulnerabilities occur when developers fail to validate, sanitize, or escape user inputs properly. This negligence allows threat actors to inject malicious scripts, which can be executed in the context of another user’s session, resulting in stolen data or compromised applications. While many developers use input sanitization as a security measure, this technique alone is insufficient. Additional security practices, such as using secure coding frameworks, are essential to mitigate XSS risks.

Action for Senior Executives and IT Leaders

CISA and the FBI are urging senior executives and IT leaders to ensure their development teams are actively working to eliminate vulnerabilities like XSS. Business leaders should take a proactive approach by asking their teams how they are integrating secure by design practices and ensuring software is free from these preventable flaws. Regular reviews of past vulnerabilities and strategic planning for future security improvements are crucial for maintaining secure systems.

Key Steps to Prevent XSS Vulnerabilities

To prevent XSS vulnerabilities, technical leaders must:

1. Review threat models** to identify and address potential vulnerabilities early.
2. Validate and sanitize inputs**, ensuring input is both structured and meaningful.
3. Utilize modern web frameworks** that provide built-in functions for secure output encoding and escaping, reducing the burden on developers to manually handle input validation.
4. Conduct rigorous code reviews** to catch security issues before deployment.
5. Implement adversarial testing** to stress-test code and identify weaknesses during development.

Secure by Design Principles

To reduce the prevalence of vulnerabilities like XSS, CISA and the FBI recommend software manufacturers follow the principles outlined in their guidance, "Shifting the Balance of Cybersecurity Risk: Principles and Approaches for Secure by Design Software."

Principle 1: Take Ownership of Customer Security Outcomes

Software manufacturers should prioritize eliminating XSS vulnerabilities from their products. By implementing secure building blocks early in development, manufacturers can prevent single coding errors from exposing millions of users to risk. This shift from reactive to proactive security, relying less on patching after-the-fact, is vital for safeguarding customer data at scale.

Automated tools, static analysis, and ongoing code reviews should be standard practice to identify and correct security weaknesses before software is deployed. Senior executives must take responsibility for ensuring their teams regularly test and review their code to guarantee it is secure by design.

Principle 2: Embrace Transparency and Accountability

Manufacturers should maintain transparency when disclosing product vulnerabilities. Tracking vulnerabilities and disclosing them to customers through the CVE (Common Vulnerabilities and Exposures) program helps create industry-wide awareness and encourages improvements in development practices. Additionally, software companies should focus on addressing the root causes of vulnerabilities, such as CWE-79, a common cause of XSS, and set business goals to eliminate these flaws entirely.

A modern vulnerability disclosure program (VDP) is essential to allow the industry and customers to identify recurring defects and track progress in eliminating these vulnerabilities. CISA provides resources to help organizations establish and maintain a VDP.

Principle 3: Build Leadership and Structure to Support Security

Technology executives must give product security the same priority as cost management. The decisions made by businesses to cut corners on security often result in increased risks for customers and the economy. By fully implementing secure by design principles, manufacturers can reduce the long-term costs of addressing vulnerabilities and the complexity of securing their systems.

Executives should invest in programs that aim to eliminate entire classes of vulnerabilities, such as XSS, instead of addressing individual instances as they arise. Ongoing reviews should be conducted to detect common vulnerabilities and ensure that mitigations are in place. Regular updates on the company’s progress in identifying and eliminating recurring vulnerabilities should be requested by leadership.

Disclaimer

The information provided in this report is for informational purposes only. The authoring organizations do not endorse any commercial entities, products, or services mentioned herein. Any reference to commercial products or services does not imply endorsement by the authoring organizations.