HTML Injection Payloads
Overview of HTML Injection
The "skeleton" of any online application is "HTML," which defines the general layout and style of the hosted material. Ever questioned what might occur if a few basic scripts were to damage this anatomy? Or does this structure begin to take the blame for web application tampering? In this post, we'll learn how these improper HTML codes enable hackers to alter carefully created websites and steal confidential data from users.
How does HTML Injection work?
A form of attack known as HTML injection occurs when malicious HTML code is added to a website. This may result in anything from small-scale website vandalism to large-scale data breaches. HTML injection, in contrast to other online vulnerabilities, attacks the markup language that serves as the foundation for the majority of websites.
This attack focuses on altering the structure and content of a webpage, which sets it apart from other online vulnerabilities that make use of server or database flaws.
Typical Reasons
One of the most frequent reasons for HTML injection is negligence. First on the list is a lack of input validation, which makes it easy for attackers to enter harmful code. Hackers with experience can also take advantage of misconfigured web servers, which provide opportunities. Finally, these assaults are made possible by careless or hurried coding techniques that are vulnerable.
Despite their seeming technicality, these reasons are frequently the result of human mistakes. The human factor is always there, whether it's a server administrator incorrectly configuring settings or a developer ignoring a security precaution.
Illustrations of HTML Injection
The following are some of the most typical instances of HTML injections:
Defacing
HTML injection's most basic use is defacing, which alters the page's visible content. To add a visual advertisement for a product they intend to sell, for instance, an attacker may utilise a cached HTML injection. Furthermore, the attacker may use malicious HTML code for personal or political gain to damage the page's reputation.
Extrapolation of private user data
Two more common uses of HTML injection are the construction of a form on the intended website and manipulating the user into providing confidential data there.
For example, a malicious code insert may be used by an attacker to show a fake login form. Afterward, the form's login and password data would be sent to a server the attacker-controlled.
If the website uses relative URLs, the hacker could try to exploit the tag to steal data. For example, all forms would be submitted to the xyz.com website, which is controlled by the attacker, if they inject, because the web page uses relative URLs to submit forms.
Theft of Anti-CSRF Tokens
Additionally, using HTML injection, attackers can take anti-CSRF tokens and utilize them in a later cross-site request forgery (CSRF) attack. The hidden input type on a form is frequently used to send anti-CSRF tokens.
To exfiltrate the token, an attacker may, for instance, utilize a non-terminated tag with single quotes, like this:
Another option is to insert a <textarea> tag. The <textarea> and <form> tags will both be implicitly closed in this case and any content that comes after the <textarea> element will be submitted.
Exfiltrating Stored Passwords in the Browser
Attackers can also incorporate forms that browser password managers will automatically fill out using HTML injections. If the attacker successfully injects the correct form, the password manager will provide the user credentials immediately. All that is needed for the form to work with multiple browsers is that the action parameter points to any host, and the input fields have the correct names and structures.
Effects of HTML Injection
HTML injection vulnerabilities are commonly disregarded. Even if HTML injections don't directly harm the web server or the database, they might still have detrimental effects like the following.
An attacker may create a fake form to trick a user into entering their login credentials or to steal password information that has been stored in the browser. If the targeted user possesses certain permissions, malicious actors may be able to access the web application on an administrative level.
If the attacker conducts a public attack, the company, organization, or even the country's reputation might be severely harmed. If a high-value page is vandalized or used as a means of spreading false information, users or clients could make unwise decisions and lose trust in your cybersecurity protocols.
The attacker may utilize HTML injection as a stepping stone to more serious attacks like CSRF.
After inserting his HTML content into malicious URLs, the attacker emails the victim the URLs. The user accesses the website since it is housed on a trustworthy domain, which allows his identity to be stolen.
HTML Injection Types
Since HTML is considered a reasonably simple language, this attack doesn't seem to be that hard to understand or execute. There are various methods to execute this sort of assault. However, reflected and stored HTML injection are the two primary types.
Stored HTML Injection
A malicious script that has been injected into a web application which is permanently saved inside the application server is called a "stored HTML" attack, which is sometimes referred to as "Persistence". When the user views the injected webpage, the application server then dumps the malicious script back out to the user. The browser will run the injected HTML code when the user clicks on the payload, which seems to be an official website element.
The most common use case for cached HTML is the "comment option" on blogs, which allows any user to submit input in the form of comments for the admin or other users.
Injection of HTML using DOM
The webpage's Document Object Model (DOM), which depicts the page's structure, is the target of the assault. Attackers can insert malicious scripts that run client-side by tampering with the DOM.
Both web developers and security experts must comprehend the DOM. It serves as a link between HTML and JavaScript, and any flaws might result in serious security lapses. The first line of defense is understanding how these assaults function.
Reflected HTML Injection
A web application generates "Reflected HTML Injection," or "Non-Persistence Vulnerability," when it responds to user input without first validating it. This allows a prospective attacker to embed browser executable code within the single HTML response. The reason it is called "non-persistent" is that the malicious script is not stored on the web server, therefore phishing must be used to disseminate the dangerous link and trick the user.
An attacker might easily put arbitrary HTML code into a website's search textbox. If the website contains a HTML vulnerability then the output page will show the HTML entities in response.
Strategies for prevention and mitigation
Validation and Sanitization of Input
Input validation and sanitization are the first lines of defense against HTML injection. Malicious inputs can be effectively blocked by ensuring that every user input is carefully checked against a predetermined criterion. This entails ensuring that data types, lengths, and patterns match expected values by inspecting them.