A Hacker One report showed that XSS attacks were the top vulnerability in recent years. You might be thinking, if XSS is such a common problem, then I probably don’t need to worry about it. But don’t be complacent. Cross-site scripting attacks can be extremely harmful.
In this article, we will discuss how XSS attacks work, how you can check if you are vulnerable, and how to prevent a cross-site scripting attack.
What is a Cross-Site Scripting Attack?
Cross-site scripting (XSS) is a security vulnerability that allows an attacker to inject malicious code scripts into web applications. These attacks can expose the end user’s personal and sensitive data as they click through seemingly trustworthy links.
XSS attacks are fairly widespread and can affect web pages, applications and even the increasingly popular conversational AI platform software. XSS attacks can lead to redirection to a malicious web page or even a full account takeover.
Types of XSS attacks
There are a few different types of XSS that you should be aware of.
Reflected
A reflected XSS attack is when the malicious script or code is injected into the URL or an HTTP response and is reflected back to the user in the response via a pop-up, error message, or similar.
This type of XSS attack is usually delivered when the user clicks on a seemingly innocent or trusted link, which then allows the malicious script to run on the victim’s browser.
Persistent
Also known as stored XSS, persistence XSS attacks happen when the application stores user input but fails to validate it before embedding it into the webpage. Sites that receive and store user content and data are, therefore, targets for persistent attacks.
A persistent attack involves the permanent storage of malicious scripts or codes on the application, site, or targeted servers. When the stored data is retrieved, the malicious scripts could then be executed as if the trusted user ran them.
DOM-based
With DOM-based attacks, the malicious code is in the source that the hacker controls in the Document Object Model (DOM). In a DOM-based attack, the malicious data is reflected by the JavaScript code.
What is the Impact of an XSS attack?
Attackers carrying out XSS attacks may have a variety of bad intentions, the impact of which could be devastating. Hackers’ intentions might be:
- To manipulate and modify content
- To redirect users to malicious content
- To impersonate users and take over accounts
- To steal personal information and data
- To infiltrate and gain control of the edge layers of your site
Any of the above will negatively impact both users and developers. What’s more, after an XSS attack, users will believe your site or application is unsafe, which can have devastating long-term effects.
If you leave yourself open to XSS attacks, you could lose clients, users and, ultimately, your integrity as a developer.
How Do You Know If You Are Vulnerable?
To understand if you are vulnerable to XSS attacks, it is worth completing an audit of all user inputs in your app. This will help you determine whether HTML outputs are not being validated or encoded. You can find free and paid tools to help with the audit process.
XSS attacks are most likely to occur when there is unscreened user input into the outputs. Any AI virtual assistant could be vulnerable to such attacks. Ensure you don’t skim over secure coding practices and filters, as this will leave your application or site vulnerable.
How to Prevent a Cross-Site Scripting Attack
Cross-site scripting is a common yet complex attack vector that can be difficult to remedy. However, by following some cyber security best practices, you can protect your application and prevent a cross-site scripting attack. This is such a widespread problem that DevSecOps roles are becoming more popular than ever.
Here, we will discuss some of the ways you can prevent a cross-site scripting attack.
- Validation
Since a successful XSS attack occurs when the attacker inserts malicious code into a webpage, one of the best ways to protect against XSS attacks is to validate every input at the point it is received.
An example of this would be if a username should be in email address format, the value of the input should contain the expected characters for an email address.
By validating inputs at the source, you can block unwanted attempts to hack into your application and ensure that only correctly structured data passes through.
- Sanitization
You can ensure user input is safe by entirely removing potentially malicious characters. This ensures that the website or application receives only trusted data.
However, the sanitization process can be difficult to implement and is prone to errors due to its complexity. With HTML sanitization, for example, content is removed based on an allow or deny list. Due to the ever-evolving possible vectors for malicious code, your deny list can become difficult to manage.
- Output Encoding
Output encoding is another way you can protect against a cross-scripting attack. This involves encoding inputs before rendering them in HTML to ensure the browser doesn’t interpret certain characters as code.
Encoding ensures that user contributions are interpreted as ordinary text rather than being executed as scripts.
- Allowlisting and Blocklisting
To further protect your websites or applications from XSS attacks, consider using an allowlisting vs blocklisting validation approach. As you may have gathered, this involves using a list of criteria to create both an allowlist and a blocklist.
Allowlisting is when only specific devices, web addresses, applications, etc., can access your networks as they have been verified as “good” and meet your predetermined criteria. Blocklisting, on the other hand, validates the data by searching for “bad” content and blocking it from gaining access.
- Use a Content Security Policy (CSP)
As well as staying on top of new technology, such as AI tools for security, developers should continue to use more traditional security methods, including a content security policy.
A content security policy restricts the scripts and images that a web page can load. Similarly to allowlisting, it only allows for approved URLs and JavaScript files. A CSP can help to detect and diminish XSS attacks but works best alongside other preventative measures.
- Use Proof of Source Authenticity (PoSA)
Proof of Source Authenticity (PoSA) gives users visible proof that webpages, links and so on are legitimate and trustworthy. It works by creating a digital watermark which appears on the site when a user visits it. Ofter, this watermark will include the brand logo. Even small businesses can fall victim to such attacks and should use effective small business tools to remain credible and trusted by customers.
Adopting PoSA technology can enhance your website’s marketing efforts by showcasing your commitment to security and authenticity. It can also protect you and your users from impersonation attacks.
- Use Vulnerability Scanning Tools
As we mentioned earlier, scanning for vulnerabilities can be one of the best ways to protect yourself against XSS attacks. They can identify security weaknesses in applications, networks and systems by scanning code and inputs. By regularly scanning and addressing these issues, you can significantly reduce your digital footprint’s exposure to XSS attacks.
Some vulnerability scanning tools that are available to you include:
- XSS Hunter
- XSStrike
- XSSER
- Acunetix
- Burp Suite
- Dalfox
- Intruder
You might compare this process to a large organization adopting quality assurance for call center processes. Becoming aware of possible problems and improving customer experiences is the aim. Once you are aware that vulnerabilities exist, you can then work to fix them.
- Use Web Application Firewalls
So you’ve gone to all the trouble of building your site, purchasing a domain from Only Domains, and launching your web page. But all of your time and energy will be wasted if it is not well protected.
A web application firewall (WAF) monitors and blocks malicious traffic before it reaches a web application. A WAF can detect and block XSS attacks in real-time. They are invaluable to developers looking to protect their applications from such attacks.
However, WAFs don’t identify the cause of the vulnerability. They are best used alongside some of the other protective factors we have discussed.
Final Thoughts
Cross-site scripting attacks are common, but this does not mean they can be ignored or underestimated. Just a singular XSS attack could be devastating to your application and to your users. If hackers obtain sensitive data, for example, your reputation can be destroyed.
Highly successful developers will follow the security best practices outlined in this article. This gives them the best chance at preventing XSS attacks and maintaining their reputation as safe and secure developers.
