CVE-2024-7525: Mozilla Firefox Privilege Escalation Flaw

CVE-2024-7525 Overview

CVE-2024-7525 is an Improper Access Control vulnerability in Mozilla Firefox, Firefox ESR, and Thunderbird that allows web extensions with minimal permissions to create a StreamFilter which can be used to read and modify the response body of HTTP requests on any website. This permission bypass vulnerability undermines the browser's extension permission model, enabling potentially malicious extensions to intercept and manipulate web traffic without requiring the appropriate host permissions.

Critical Impact

A malicious web extension with only basic permissions could intercept, read, and modify sensitive data transmitted between users and any website, enabling credential theft, session hijacking, or injection of malicious content.

Affected Products

• Mozilla Firefox versions prior to 129
• Mozilla Firefox ESR versions prior to 115.14 and 128.1
• Mozilla Thunderbird versions prior to 115.14 and 128.1

Discovery Timeline

• August 6, 2024 - CVE-2024-7525 published to NVD
• August 12, 2024 - Last updated in NVD database

Technical Details for CVE-2024-7525

Vulnerability Analysis

This vulnerability stems from improper access control (CWE-284) and incorrect default permissions (CWE-276) in Mozilla's web extension API implementation. The StreamFilter API, which is designed to allow extensions to intercept and modify HTTP response data, failed to properly validate that the calling extension had the necessary host permissions before allowing stream interception.

Under normal operation, web extensions must declare specific host permissions in their manifest to access content from particular websites. However, the flawed implementation allowed extensions with minimal or no host permissions to create StreamFilter objects capable of intercepting traffic from any origin. This fundamentally breaks the principle of least privilege that the extension permission model is designed to enforce.

The vulnerability requires user interaction in the form of installing a malicious extension, but once installed, the extension could silently intercept all web traffic without any additional user consent or visible indication.

Root Cause

The root cause is improper permission validation in the StreamFilter API implementation. When an extension attempts to create a StreamFilter, the browser should verify that the extension has been granted permission to access the target host. The vulnerable code path bypassed this permission check, allowing any extension—regardless of its declared permissions—to create filters for arbitrary hosts.

This represents both an improper access control issue (CWE-284) where the access control mechanism was insufficient, and an incorrect default permissions issue (CWE-276) where the default behavior was overly permissive.

Attack Vector

The attack requires a network-based vector where an attacker distributes a malicious browser extension. The extension would appear benign, requesting only minimal permissions during installation. Once installed, the extension can leverage the StreamFilter vulnerability to intercept HTTP response bodies from any website the user visits.

An attacker could use this capability to steal authentication tokens, credentials, or sensitive data from HTTPS connections; inject malicious JavaScript into legitimate web pages; modify financial transaction data or form submissions; and exfiltrate browsing activity and personal information.

The attack leverages the browser extension API to create unauthorized stream filters, enabling interception and modification of web traffic without proper permission grants. For detailed technical implementation, refer to Mozilla Bug Report #1909298.

Detection Methods for CVE-2024-7525

Indicators of Compromise

• Installed browser extensions using StreamFilter API without corresponding host permissions in manifest
• Unexpected network traffic interception or modification by browser extensions
• Extensions with minimal permissions making cross-origin data access attempts
• Anomalous extension behavior observed in browser developer tools network panel

Detection Strategies

• Audit all installed browser extensions for suspicious permission configurations
• Monitor extension API usage patterns for browser.webRequest.filterResponseData() calls
• Review browser extension source code for StreamFilter usage without appropriate permission declarations
• Implement endpoint detection rules for browser processes creating unauthorized stream filters

Monitoring Recommendations

• Enable enterprise browser management to track and approve extension installations
• Deploy browser telemetry monitoring to detect anomalous extension API calls
• Implement content security policies to limit extension capabilities where possible
• Regularly review browser extension inventories across endpoints for unauthorized or suspicious extensions

How to Mitigate CVE-2024-7525

Immediate Actions Required

• Update Mozilla Firefox to version 129 or later immediately
• Update Mozilla Firefox ESR to version 115.14 or 128.1 or later
• Update Mozilla Thunderbird to version 115.14 or 128.1 or later
• Audit installed browser extensions and remove any suspicious or unnecessary extensions
• Restrict browser extension installation through group policy in enterprise environments

Patch Information

Mozilla has released security patches addressing this vulnerability across all affected product lines. Detailed information is available in the following security advisories:

• Mozilla Security Advisory MFSA-2024-33
• Mozilla Security Advisory MFSA-2024-34
• Mozilla Security Advisory MFSA-2024-35
• Mozilla Security Advisory MFSA-2024-37
• Mozilla Security Advisory MFSA-2024-38

Workarounds

• Disable or uninstall untrusted browser extensions until patching is complete
• Restrict extension installation to approved extensions only via enterprise policy
• Use browser profiles without extensions for sensitive browsing activities
• Enable strict site isolation features to limit cross-origin data access

# Firefox Enterprise Policy Configuration (policies.json)
# Place in Firefox installation directory or distribution folder
{
  "policies": {
    "ExtensionSettings": {
      "*": {
        "installation_mode": "blocked"
      }
    },
    "DisableAppUpdate": false,
    "DisableTelemetry": false
  }
}