CVE-2025-8031: Leakage of HTTP Basic Authentication Credentials in Firefox and Thunderbird

Overview

CVE-2025-8031 is a critical vulnerability affecting numerous versions of popular web browser Firefox and email client Thunderbird. This vulnerability arises from a flaw in the handling of URLs in CSP (Content Security Policy) reports, which can potentially lead to leakage of HTTP Basic Authentication credentials. Given the widespread use of these applications across a variety of sectors, the impact of this vulnerability is significant. The leakage of authentication credentials can lead to unauthorized access to sensitive systems and data, and therefore, it is of utmost importance to address this vulnerability immediately.

Vulnerability Summary

CVE ID: CVE-2025-8031
Severity: Critical, CVSS 9.8
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Leakage of HTTP Basic Authentication credentials, potential system compromise or data leakage

Affected Products

Product | Affected Versions

Firefox | < 141 Firefox ESR | < 128.13, < 140.1 Thunderbird | < 141, < 128.13, < 140.1 How the Exploit Works

This vulnerability arises due to a flaw in the stripping of the `username:password` part of URLs in CSP reports. When a user accesses a site that requires HTTP Basic Authentication, the credentials are transmitted in the HTTP header. The software fails to properly sanitize these credentials from CSP reports, potentially leaking them to third parties. An attacker could exploit this vulnerability by intercepting the CSP reports and extracting the credentials.

Conceptual Example Code

Below is a conceptual representation of how an HTTP request could look like when processed by a vulnerable system:

GET /test/report HTTP/1.1
Host: vulnerable.example.com
Authorization: Basic QWxhZGRpbjpPcGVuU2VzYW1l
Content-Security-Policy-Report-Only: default-src 'self'; report-uri /csp-report-endpoint;

In this case, the `Authorization` header contains the base64 encoded username and password (`Aladdin:OpenSesame`). The `Content-Security-Policy-Report-Only` header sets the CSP in report-only mode and specifies the endpoint (`/csp-report-endpoint`) to which the browser should send reports about policy violation.
An attacker, monitoring network traffic or having access to the report endpoint, could intercept this request, decode the `Authorization` header, and extract the credentials.

Remediation Steps

The recommended mitigation for this vulnerability is to apply the vendor patch. However, if immediate patching is not possible, implementing a Web Application Firewall (WAF) or Intrusion Detection System (IDS) could serve as a temporary mitigation, providing some level of protection against potential attacks exploiting this vulnerability.