CVE-2026-18809 Overview
CVE-2026-18809 is an information disclosure vulnerability affecting Mozilla Firefox for Android and Firefox Focus for Android. The flaw is categorized under [CWE-200] (Exposure of Sensitive Information to an Unauthorized Actor). An attacker can leverage the issue over the network when a user interacts with malicious content, exposing sensitive data from the browser context.
Mozilla addressed the issue in Firefox 153.0.3. The vulnerability is tracked in Mozilla Security Advisory MFSA-2026-73 and Mozilla Bugzilla entry 2055683.
Critical Impact
Successful exploitation leaks sensitive information from Firefox for Android or Firefox Focus for Android to a remote attacker when the victim interacts with attacker-controlled content.
Affected Products
- Mozilla Firefox for Android (versions prior to 153.0.3)
- Mozilla Firefox Focus for Android (versions prior to 153.0.3)
Discovery Timeline
- 2026-08-04 - CVE-2026-18809 published to the National Vulnerability Database
- 2026-08-04 - Last updated in NVD database
Technical Details for CVE-2026-18809
Vulnerability Analysis
CVE-2026-18809 is an information disclosure weakness in the Android builds of Firefox and Firefox Focus. The flaw maps to [CWE-200], indicating the browser exposes sensitive data to a party that should not have access to it. Exploitation requires a network-reachable attacker and user interaction, such as visiting a crafted page or opening a malicious link.
Mozilla resolved the issue in Firefox 153.0.3. The advisory (MFSA-2026-73) confirms the mobile-only scope. Because the flaw impacts confidentiality without affecting integrity or availability, attackers gain read access to data the browser should isolate from the origin under attacker control.
Root Cause
Mozilla has not published a detailed technical breakdown outside the referenced advisory. The classification under [CWE-200] indicates that the affected browser code path exposes sensitive information across a boundary that should have blocked such disclosure. Further technical detail is available in the Mozilla Bug Report #2055683 and the Mozilla Security Advisory MFSA-2026-73.
Attack Vector
The attack vector is network-based and requires a user to interact with attacker-controlled content, typically a web page loaded in Firefox for Android or Firefox Focus for Android. No authentication or elevated privileges are required. Once the user visits the malicious resource, the flaw leaks sensitive browser or user data to the attacker.
No public exploit, proof of concept, or CISA KEV entry is currently associated with CVE-2026-18809. Refer to the vendor advisory for verified technical details.
Detection Methods for CVE-2026-18809
Indicators of Compromise
- Firefox for Android or Firefox Focus for Android installations reporting a version earlier than 153.0.3 in mobile device management (MDM) inventory.
- Outbound mobile browser traffic to unfamiliar domains immediately after users open links from email, SMS, or messaging apps.
Detection Strategies
- Query MDM and endpoint inventory sources for Firefox package versions and flag any Android device running a build below 153.0.3.
- Correlate mobile browser telemetry with threat-intelligence feeds to identify user interaction with suspected malicious URLs.
- Review web proxy logs for Android user-agent strings visiting newly registered or low-reputation domains hosting active content.
Monitoring Recommendations
- Track Mozilla security advisory feeds, including MFSA-2026-73, for updates on scope and any follow-up fixes.
- Monitor EPSS trending; the current EPSS value is low but should be reassessed if public exploit code appears.
- Alert on Android devices that remain on unpatched Firefox versions beyond your defined patch SLA.
How to Mitigate CVE-2026-18809
Immediate Actions Required
- Update Firefox for Android and Firefox Focus for Android to version 153.0.3 or later through Google Play or the vendor distribution channel used in your environment.
- Push the update via MDM to enforce compliance on managed Android fleets.
- Advise users to avoid opening untrusted links in the affected browsers until the update is applied.
Patch Information
Mozilla fixed CVE-2026-18809 in Firefox 153.0.3. Details are documented in the Mozilla Security Advisory MFSA-2026-73 and the associated Mozilla Bug Report #2055683. Apply the update on all Android devices running Firefox or Firefox Focus.
Workarounds
- Restrict use of Firefox for Android and Firefox Focus for Android to trusted sites until the patch is installed.
- Use MDM policies to block the launch of vulnerable browser versions where feasible.
- Enable network-level URL filtering to reduce exposure to malicious content on mobile devices.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
