CVE-2025-8042: Mozilla Firefox Information Disclosure Flaw

CVE-2025-8042 Overview

A critical vulnerability has been identified in Firefox for Android that allows sandboxed iframes to bypass download restrictions. Specifically, an iframe without the allow-downloads attribute can still initiate downloads, circumventing a fundamental browser security control. This flaw undermines the sandbox isolation model that web developers rely on to restrict the capabilities of embedded content, potentially enabling malicious websites to silently download files to a user's device without proper authorization.

Critical Impact

Attackers can exploit sandboxed iframes on malicious websites to initiate unauthorized file downloads to Android devices, potentially leading to malware installation, drive-by downloads, or exploitation of other mobile vulnerabilities through downloaded payloads.

Affected Products

• Mozilla Firefox for Android versions prior to 141
• Google Android operating system (as the underlying platform)
• Web applications relying on iframe sandbox download restrictions

Discovery Timeline

• 2025-08-19 - CVE-2025-8042 published to NVD
• 2025-09-19 - Last updated in NVD database

Technical Details for CVE-2025-8042

Vulnerability Analysis

This vulnerability stems from improper permission assignment (CWE-732) in Firefox for Android's sandbox implementation. The HTML5 sandbox attribute on iframes is designed to impose strict restrictions on embedded content, including the ability to prevent downloads unless the allow-downloads keyword is explicitly specified. Firefox for Android failed to properly enforce this restriction, allowing sandboxed iframes to initiate file downloads regardless of whether the allow-downloads permission was granted.

The flaw represents a critical break in the browser's security model. When developers embed untrusted third-party content within sandboxed iframes, they expect the sandbox restrictions to prevent potentially malicious actions. By bypassing the download restriction, an attacker hosting malicious content within a sandboxed iframe can force downloads of malicious files to the user's device.

Root Cause

The root cause is classified as CWE-732: Incorrect Permission Assignment for Critical Resource. The Firefox for Android download handling component did not properly check the sandbox flags before allowing download requests initiated from iframe contexts. The permission validation logic failed to account for the allow-downloads directive when processing download intents from sandboxed content.

Attack Vector

This is a network-based attack that requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Creating a malicious webpage that embeds attacker-controlled content within a sandboxed iframe (explicitly without the allow-downloads permission)
2. The iframe content then initiates a download request, which should be blocked by the sandbox
3. Due to the vulnerability, Firefox for Android processes the download request despite the sandbox restrictions
4. The malicious file is downloaded to the victim's Android device

The attack can be delivered through compromised websites, malvertising campaigns, or phishing links. When a user visits the malicious page using a vulnerable Firefox for Android version, the download occurs automatically without proper security checks.

Detection Methods for CVE-2025-8042

Indicators of Compromise

• Unexpected file downloads appearing on Android devices without explicit user consent
• Browser logs showing download requests originating from sandboxed iframe contexts
• Network traffic indicating file downloads initiated from iframe sources that should have restricted permissions
• Downloaded files with suspicious origins traced back to sandboxed iframe content

Detection Strategies

• Monitor for unexpected download activity on mobile devices running Firefox for Android versions prior to 141
• Implement network-level monitoring to detect downloads initiated from known malicious domains
• Review application logs for download requests that bypass standard user authorization flows
• Deploy mobile threat detection solutions that can identify suspicious download patterns

Monitoring Recommendations

• Enable browser telemetry and logging where possible to track download origins
• Implement endpoint detection solutions on managed Android devices
• Monitor for unusual file types being downloaded through the browser
• Track Firefox version deployment across the organization to identify vulnerable instances

How to Mitigate CVE-2025-8042

Immediate Actions Required

• Upgrade Firefox for Android to version 141 or later immediately
• Audit managed device fleet to identify systems running vulnerable Firefox versions
• Consider temporarily restricting Firefox for Android usage on managed devices until patching is complete
• Alert users to the risk of visiting untrusted websites until the browser is updated

Patch Information

Mozilla has addressed this vulnerability in Firefox version 141. The security update is detailed in Mozilla Security Advisory MFSA-2025-56. Users should update Firefox for Android through the Google Play Store or their organization's mobile device management system. Additional technical details are available in Mozilla Bug Report #1791322.

Workarounds

• If immediate patching is not possible, consider using alternative mobile browsers until Firefox can be updated
• Employ mobile device management policies to restrict browser access to trusted sites only
• Enable download prompts and disable automatic downloads in browser settings where available
• Use network-level filtering to block downloads from untrusted sources

# Verify Firefox version on managed Android devices (via adb)
adb shell dumpsys package org.mozilla.firefox | grep versionName
# Ensure version is 141 or higher to be protected against CVE-2025-8042