Overview
The cybersecurity landscape is continuously evolving, and a new vulnerability that needs immediate attention has been identified. CVE-2025-6433 is a severe cybersecurity flaw that affects Firefox users running versions earlier than 140. This vulnerability is significant because it allows a malicious actor to bypass TLS certificate validation, violating the WebAuthn specification, a core security layer for web applications. The potential consequences include system compromise and data leakage, underlining the urgency of addressing this vulnerability.
Vulnerability Summary
CVE ID: CVE-2025-6433
Severity: Critical (CVSS 9.8)
Attack Vector: Network
Privileges Required: None
User Interaction: Required
Impact: System compromise or data leakage
Affected Products
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Product | Affected Versions
Firefox | < 140 How the Exploit Works
The vulnerability exploits a flaw in Firefox’s handling of invalid TLS certificates. When a user visits a webpage with an invalid TLS certificate and grants an exception, the webpage can provide a WebAuthn challenge that the user is prompted to complete. This bypasses the standard secure transport requirement of the WebAuthn specification and establishes a connection that can be exploited for malicious purposes.
Conceptual Example Code
The following pseudocode illustrates how the vulnerability might be exploited. In this example, a user visits a malicious website that provides an invalid TLS certificate. When the user grants an exception, the website issues a WebAuthn challenge, allowing a malicious actor to compromise the system or leak data.
GET /malicious_website HTTP/1.1
Host: malicious.example.com
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:139.0) Gecko/20100101 Firefox/139.0
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Upgrade-Insecure-Requests: 1
HTTP/1.1 200 OK
Content-Type: text/html
Transfer-Encoding: chunked
Connection: keep-alive
Content-Security-Policy: upgrade-insecure-requests
X-Content-Type-Options: nosniff
Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
X-Powered-By: PHP/7.4.3
Server: Apache/2.4.41 (Ubuntu)
<html>
<head>
<script>
var options = {
challenge: Uint8Array.from(atob("..."), c=>c.charCodeAt(0)),
rp: { id: "malicious.example.com", name: "Malicious Site" },
user: { id: Uint8Array.from(atob("..."), c=>c.charCodeAt(0)), name: "victim", displayName: "Victim" },
pubKeyCredParams: [{ type: "public-key", alg: -7 }]
};
navigator.credentials.create({ publicKey: options })
.then(function (attestation) {
console.log(attestation);
})
.catch(function (error) {
console.log(error);
});
</script>
</head>
<body>
</body>
</html>Remember, this is a conceptual example. The actual exploit would involve complex code and a sophisticated understanding of both the WebAuthn specification and Firefox’s implementation of it.