Microsoft engineers introduced cross-site scripting (XSS) in January 2000, and it’s been one of the most common cyber threats ever since.
It’s a broad term that encompasses any form of script injection through a third-party site. It can be used to compromise sensitive data, mimic website behavior, and force applications to behave in ways they otherwise wouldn’t. Organizations can implement a few simple practices to mitigate their risk of suffering a cross-site scripting attack. Still, failure to do so could leave them with an enlarged attack surface—and, eventually, a breach.
In this article, we’ll define cross-site scripting attacks in more detail and show you some steps you can take to identify and remediate any XSS vulnerabilities present within your environment.
The Open Worldwide Application Security Project (OWASP) defines cross-site scripting as “a type of injection in which malicious scripts are injected into otherwise benign and trusted websites.” XSS first referred to stealing data from one site or application to another, but its range has now widened to include any form of unauthorized content injection.
To articulate that shift, OWASP’s most recent report, “OWASP Top 10 2021,” categorized XSS tactics as a subset of a broader threat known as injection attacks. Within that category, XSS attacks were identified under Common Weakness Enumeration 79 (CWE-79), which elaborates on the practice in more detail.
Injection attacks fell from the first to third most common vulnerability but still had a max incident rate of 19.09% at over 274,000 occurrences. Since XSS attacks comprise a significant portion of these, guarding against this cyber threat remains essential to maintaining an effective security posture.
According to the MITRE Organization, cross-site scripting attacks occur when “the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.” Hackers can exploit this vulnerability by using some type of web application to send malicious code to a different end—user, typically with a browser-side script.
More specifically, XSS attacks happen when:
Essentially, XSS attacks are a form of code interception where the attacker secretly inserts malicious scripts between the user and the application.
XSS attacks can be very diverse, so it’s essential to understand the different types that exist to maintain protection from each one. Cross-scripting attacks are classified as Type 1, Type 2, and, less commonly, Type 0. The differences are:
However the XSS attacks are achieved, hackers can use them for multiple nefarious purposes, including:
Once attackers have used XSS tactics to infiltrate a network, they can move laterally to access other system parts. That’s why remediating a team’s XSS-related vulnerabilities can strengthen their entire IT environment.
There’s no single practice that eliminates cross-scripting attacks. Instead of adopting a one-size-fits-all approach, teams should implement various best practices to mitigate their XSS attack surface. OWASP’s Cross-Site Scripting Prevention Cheat Sheet gives thorough guidelines on how teams may best protect themselves from XSS attacks, but some of the most common best practices are:
Integrating code security tools into the internal development environment (IDE) can help identify and remediate any current XSS-related vulnerabilities. Static application security testing (SAST) tools help resolve vulnerabilities in proprietary code before runtime, and static code analysis (SCA) software can shore up known weaknesses in open-source code.
Both code security tools help developers protect and sanitize their variables, and both can close potential injection sites where attackers could insert malicious scripts. That makes SAST and SCA code security tools essential for thwarting cross-site scripting attacks.
Although the threat landscape continues to grow more complex, cyber attackers still often resort to the most time-tested tricks—and one of them is cross-site scripting. Output encoding, safe sink installation, and protecting and sanitizing all variables are a few best practices that can help you reduce your XSS attack surface. However, integrating code security tools into your current IDE is also essential. Kiuwan’s SAST and SCA tools help developers detect and remediate vulnerabilities within their code, making it harder for threat actors to inject their own. Our solutions can strengthen your defenses against cross-site scripting attacks while improving your code quality and security, so request a demo today to see what we offer.
