Security risks of iframes: Protecting your app from potential attacks

Many developers use iframes because they make embedding things like videos, maps, or social media feeds super easy. You can pull in content from other sites without messing with your own code too much. They help keep things neat, too—since the embedded content is separate, it won’t mess with your site’s layout or design. Plus, iframes are a great way to get around the whole same-origin policy when you want to bring in content from a different domain.

While the concept may sound simple and convenient, the security implications of embedding external content can be severe if not handled correctly.

What is an iframe?

An iframe is a window embedded within a webpage that can display content from a different website or source. This allows developers to integrate third-party content—such as videos, advertisements, or external widgets—into their webpages seamlessly.

For example, this webpage uses an iframe to display this YouTube video:

The code to do this looks like this:

	
<iframe width="560" height="315" src="https://www.youtube.com/embed/237vaK_nYRg" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
	

This HTML tag creates a window that loads the YouTube video player and allows users to interact with it, such as play, pause, or adjust the volume, without leaving the page.

Are all iframes dangerous?

Not all iframes are equally dangerous. The key risk lies in what content is being loaded within the iframe and how it interacts with the rest of the webpage.

For example, embedding a YouTube video (or other similar trusted platforms like Vimeo) is typically not dangerous. YouTube controls the content within their iframe, and their video player is designed with security measures to prevent harmful actions. If you are certain that the source URL comes from a trusted domain, then you can rest assured that the iframe doesn't point to malicious content (unless the source is hacked).

However, when iframes are used to load external forms (e.g., user signup, login forms, or payment pages), they can be more dangerous as they open the door to a number of vulnerabilities if not implemented properly. Let’s see some of them.

Cross-site scripting (XSS) vulnerabilities

One of the most significant security concerns with iframes is the potential for Cross-Site Scripting (XSS) attacks. In a typical XSS attack, an attacker injects malicious scripts into a website, which are then executed in the context of the user’s browser. If you embed a third-party iframe that hosts untrusted or user-generated content, there’s a risk that malicious code could be executed within the iframe.

This could lead to:

• The theft of sensitive user data, such as login credentials or personal information.
• Unauthorized manipulation of the parent page, compromising the integrity of your website.
• Phishing attacks that trick users into entering personal information into a malicious form embedded within the iframe.

Clickjacking attacks

In a clickjacking attack, malicious actors trick users into clicking on something different from what they perceive on a webpage. By embedding a transparent iframe over a legitimate webpage, an attacker can deceive users into interacting with hidden elements, such as buttons or forms, without their knowledge.

For example, a user might think they are clicking a harmless button on your website, but they could actually be authorizing a financial transaction or revealing sensitive information. Clickjacking can cause severe damage to both your website's reputation and your users' security.

Session hijacking attacks

Session hijacking is a serious security risk that can occur when an attacker gains unauthorized access to a user's session on a website.

In the context of iframes, session hijacking can occur when an attacker uses an embedded iframe to load a malicious website that targets the session cookies or authentication tokens of the user. For example, if a user is logged into a website, and an iframe on that site loads content from a malicious source, the attacker can exploit vulnerabilities in the iframe or the session management system to capture session cookies or tokens, impersonate the user, and take control of their session.

This is particularly concerning if the iframe is embedded from an untrusted, insecure, or compromised third-party website. If an attacker gains access to a session cookie (which often contains sensitive data or is used for authentication), they could perform actions as the user without their knowledge, leading to identity theft, unauthorized transactions, or other malicious activities.

Cross-frame scripting (CFS) attacks

Cross-Frame Scripting (XFS) is a security vulnerability that allows attackers to manipulate or interact with the content of an iframe embedded in a different website. It’s a subset of Cross-Site Scripting (XSS), but it specifically targets interactions between different frames on a webpage.

The risk arises because web browsers typically allow JavaScript running in one frame (like the parent or a different embedded iframe) to access and interact with the content of another frame, especially if both are hosted on the same domain. However, if one of the frames is from an untrusted or malicious source, this behavior can be exploited. The attacker can inject malicious scripts or steal data by manipulating the iframe’s content, even if it’s not directly visible to the user.

For instance, a malicious iframe might exploit XFS vulnerabilities to interact with other frames on the page, access cookies, or manipulate the page’s DOM in ways that aren't apparent to the user. It can also enable phishing attacks, where the attacker can inject forms that appear to be from a trusted source, tricking users into submitting sensitive information.

Phishing and social engineering attacks

When a login form or sensitive data entry form is embedded in an iframe, it becomes easier for attackers to spoof trusted interfaces. By embedding a malicious iframe that mimics the look and feel of a legitimate site, attackers can trick users into unknowingly entering their credentials, credit card details, or other personal information.

For instance, a website might have an iframe embedded with a login form that appears to come from a trusted source, like a bank or email provider. However, this form is actually controlled by an attacker. When users enter their information, it is sent to the malicious site instead of the trusted service, giving attackers access to the user’s credentials. This type of phishing attack is harder for users to recognize, as the form might look nearly identical to the legitimate interface.

Because of these risks, many high-security services—like banks, payment processors, and other financial institutions—block iframe embedding entirely. These services prefer to direct users to their own secure login pages, preventing the potential for an attacker to use iframes for social engineering or credential theft.

Cross-site request forgery (CSRF) attacks

Cross-Site Request Forgery (CSRF) is a type of attack where an attacker tricks a user into performing an unintended action on a website they’re authenticated to. While CSRF attacks are most commonly associated with forms and cookies, iframes can also play a role. If a malicious iframe is used to load a form or make a request from a trusted site, it could cause actions (such as transferring money or changing account settings) to be taken without the user's consent.

Even if the iframe itself is from a reputable source, vulnerabilities in the third-party content can expose your website to CSRF risks.

Data privacy risks

When embedding content from third-party websites through iframes, you are essentially giving these external sites access to your users' browsing behavior. This introduces data privacy risks, especially if the third-party provider is tracking user activity or collecting personal data without proper consent. Depending on the laws and regulations in your region (like GDPR in the European Union), this could lead to legal complications.

In addition, some malicious iframes might be used to track users across websites, leading to data leakage or privacy violations. Even if the iframe content is from a legitimate source, data privacy concerns are still a risk.

Other issues

• Performance and reliability issues: When embedding external content, your website's loading times can increase significantly, as the browser must fetch and render content from a remote source. This can create a poor user experience, leading to frustration and higher bounce rates. Furthermore, if the external site embedded in the iframe goes down or experiences technical difficulties, it could impact your website's functionality. iframes introduce an additional dependency, and any failure on the external site can cause your content to break or display incorrectly.
• Compromised parent-child relationship: An iframe creates a "parent-child" relationship between the hosting page and the content inside the iframe. This relationship can be exploited if an attacker can manipulate the child (embedded) content. For instance, malicious JavaScript within an iframe can break out of its sandboxed environment and gain access to the parent website, leading to potential data theft, website defacement, or further attacks.
• Limited control and auditing: When you embed content via iframes, you are trusting an external source to provide that content safely and securely. However, you have limited control over what’s being loaded within the iframe. This is particularly dangerous if the embedded content changes dynamically or if you rely on an external service that doesn’t consistently follow secure coding practices. Without constant auditing and verification, you risk exposing your users to harmful content that you cannot fully monitor or control.

Best practices for iframes

While it's difficult to make iframes 100% secure, there are several best practices to reduce their security risks significantly:

• Use the sandbox attribute: The sandbox attribute provides a way to restrict the actions of the content inside the iframe, improving security. This can help prevent form submissions, script execution, and access to the parent page. Example: <iframe src="example.com" sandbox="allow-scripts allow-same-origin"></iframe>. You can customize the restrictions based on your needs:
  • allow-forms: Allows the iframe to submit forms.
  • allow-scripts: Allows the iframe to run scripts.
  • allow-same-origin: Allows the iframe to be treated as the same origin.
  • allow-popups: Allows popups to be opened from the iframe.
• Set proper HTTP headers: Use security headers like X-Frame-Options and Content-Security-Policy (CSP) to prevent clickjacking and restrict what can be embedded. Enable secure flags for session cookies, such as HttpOnly and Secure. This ensures that cookies cannot be accessed by JavaScript and can only be transmitted over HTTPS connections.
• Validate sources: Always ensure the content inside the iframe comes from trusted, verified sources, and avoid embedding from untrusted or external sources that could serve malicious code.
• Use HTTPS: Ensure both the parent site and the iframe content are loaded over HTTPS to prevent man-in-the-middle attacks.
• Enforce same-origin policy: Make sure that all iframes are served from the same trusted origin as your site, or use CORS (Cross-Origin Resource Sharing) to properly handle cross-origin requests.
• Implement Content Security Policy (CSP): This can limit how scripts and content are loaded in frames, reducing the chances of malicious code being executed.
• Use loading="lazy" for performance: To improve performance, you can delay loading the iframe until it's needed by using the loading="lazy" attribute. This reduces the initial page load time.
• Limit allow permissions: Be cautious about the permissions you grant to an iframe using the allow attribute. Only allow the permissions that are necessary for the functionality you require.
• Regularly audit embedded content: Ensure that any third-party content (e.g., a widget or external service) embedded via an iframe is regularly updated and monitored for security issues. Vulnerabilities can emerge in third-party libraries or services that you're embedding.
• Whenever possible, avoid embedding login forms or sensitive forms via iframes. Always redirect users to a separate, trusted login page hosted on a legitimate website.

Conclusion

While iframes are useful for embedding third-party content, they present a number of security risks, like Cross-Site Scripting (XSS), clickjacking, Cross-Frame Scripting (XFS), session hijacking, and phishing & social engineering attacks. These risks can compromise the security of your website and the personal data of your users.

By embedding login forms or forms requesting sensitive information in iframes, you increase the risk of phishing attacks, where users might unknowingly enter their credentials into a malicious form controlled by attackers. This is one of the reasons why high-security services like banks and financial institutions block iframe embedding altogether.

If you must use iframes, it's crucial to implement security best practices such as using the sandbox attribute, enforcing HTTPS, and protecting against clickjacking with X-Frame-Options. Additionally, avoiding the embedding of forms that request sensitive data and educating users on phishing risks can help mitigate these threats. In cases where iframes are absolutely necessary, alternative solutions like APIs or direct embedding with proper validation should be considered to ensure the safety of your app and its users.