CVE-2026-84135: Firefox Focus for Android Security Issue

CVE-2026-84135 Overview

CVE-2026-84135 is a security issue affecting Mozilla Firefox Focus for Android. Mozilla addressed the flaw in Firefox 155 and documented it in Mozilla Security Advisory MFSA-2026-82. The advisory categorizes this as an "Other issue" without further classification in the public record, and no Common Weakness Enumeration (CWE) identifier has been assigned. Tracking details are maintained under Mozilla Bug Report #2046661.

Critical Impact
Users of Firefox Focus for Android running versions prior to 155 remain exposed until the browser is updated through the Google Play Store or Mozilla's official distribution channels.

Affected Products

Mozilla Firefox Focus for Android (versions prior to 155)

Discovery Timeline

2026-09-01 - CVE-2026-84135 published to the National Vulnerability Database (NVD)
2026-09-01 - Last updated in NVD database

Technical Details for CVE-2026-84135

Vulnerability Analysis

Mozilla's advisory describes this entry as an "Other issue" in Firefox Focus for Android without providing detailed technical breakdown in the public record. The absence of a CWE mapping and CVSS vector reflects Mozilla's disclosure practice of grouping lower-impact browser hardening fixes under a generic category. Firefox Focus is Mozilla's privacy-focused mobile browser, so the affected code paths are limited to the Android mobile client and do not extend to desktop Firefox or Firefox for iOS.

The EPSS model estimates a probability of 0.133% that this issue will be exploited in the wild within the next 30 days, placing it in the lower percentile range of tracked vulnerabilities. No public proof-of-concept, exploit code, or in-the-wild abuse has been reported.

Root Cause

Mozilla has not published root-cause details for CVE-2026-84135 beyond confirming the fix shipped in Firefox 155. Readers requiring implementation-level context should consult Mozilla Bug Report #2046661, which may become viewable after Mozilla's standard embargo period.

Attack Vector

The attack vector is not documented in the current NVD entry. Firefox Focus for Android issues typically require the user to load attacker-controlled web content or interact with a crafted page. No code example is provided because no verified proof-of-concept has been published.

Detection Methods for CVE-2026-84135

Indicators of Compromise

No public indicators of compromise have been associated with CVE-2026-84135.
Mozilla has not released hashes, network signatures, or exploit artifacts tied to this advisory.

Detection Strategies

Inventory Android endpoints and mobile device management (MDM) records to identify installations of Firefox Focus with a version string below 155.
Correlate Google Play Store update telemetry with device compliance policies to flag devices that have not received the fixed build.

Monitoring Recommendations

Monitor Mozilla's security advisories page for updates to MFSA-2026-82 as additional technical detail is released.
Track mobile browser update compliance through your MDM or unified endpoint management platform.
Alert on Android devices where Firefox Focus remains pinned to an outdated version despite available updates.

How to Mitigate CVE-2026-84135

Immediate Actions Required

Update Firefox Focus for Android to version 155 or later through the Google Play Store.
Enforce automatic application updates on managed Android devices via MDM policy.
Confirm patch adoption across the fleet before closing the remediation ticket.

Patch Information

Mozilla fixed CVE-2026-84135 in Firefox 155. Refer to Mozilla Security Advisory MFSA-2026-82 for the authoritative fix reference. No backported patch is documented for earlier release lines.

Workarounds

No vendor-supplied workaround is documented; upgrading to Firefox Focus 155 is the recommended remediation.
Users unable to update immediately should avoid loading untrusted web content in Firefox Focus and consider an alternative up-to-date mobile browser in the interim.