CVE-2020-6830: 
NixOS vulnerability analysis and mitigation

CVE-2020-6830 is a security vulnerability discovered in Firefox for iOS version 24.1 that affects the native-to-JS bridging functionality. The vulnerability was disclosed on May 1, 2020, and was fixed in Firefox for iOS version 25. The issue involves the exposure of a security token used for communication between WKWebView and ViewController (Mozilla Security).

The vulnerability exists in the way Firefox iOS implements communication between WKWebView and ViewController using window.webkit.messageHandlers. The application uses a SECURITY_TOKEN (UUID) to protect this communication, but a web page could override the window.webkit object, allowing attackers to intercept the security token. The vulnerability has a CVSS score of 5.0 and is rated as having moderate severity (Mozilla Bugzilla).

When exploited, this vulnerability could allow an attacker's webpage to capture the security token used for native-to-JS bridging communication. While the messages themselves were not directly exploitable, the leak of the security token compromised an intended security layer (Mozilla Bugzilla).

The vulnerability could be exploited by creating a malicious webpage that overrides the window.webkit object to intercept communications between the browser and native code. A proof of concept was demonstrated showing how an attacker could capture the SECURITY_TOKEN when a user visits a specially crafted website (Mozilla Bugzilla).

The issue was fixed in Firefox for iOS version 25 by removing the use of the security token for JS-to-native communications while maintaining it for native-to-JS operations. The fix was implemented because the token was found to be unnecessary for JS-to-native communications and its presence was actually creating a security risk (Mozilla Security).