CVE-2026-8706: Mozilla Firefox Information Disclosure Flaw

CVE-2026-8706 Overview

CVE-2026-8706 is an information disclosure vulnerability in Firefox for iOS. The browser hosted its Reader mode on an unauthenticated local web server. Any other application installed on the same device could connect to that server and request arbitrary URLs. The local server then fetched those URLs using the signed-in user's session cookies and returned the rendered response. This exposed authenticated content to unauthorized local applications. Mozilla fixed the issue in Firefox for iOS 151.0 and tracks it under advisory MFSA-2026-49. The weakness maps to [CWE-200: Exposure of Sensitive Information to an Unauthorized Actor].

Critical Impact

A co-resident application on an iOS device can retrieve authenticated web content, including session-protected pages, by issuing requests through Firefox's local Reader mode server.

Affected Products

• Mozilla Firefox for iOS prior to 151.0
• iOS devices with Firefox installed alongside other applications
• Users signed into web services through Firefox for iOS

Discovery Timeline

• 2026-05-19 - CVE-2026-8706 published to NVD
• 2026-05-20 - Last updated in NVD database

Technical Details for CVE-2026-8706

Vulnerability Analysis

Firefox for iOS implemented its Reader mode feature by running a local web server inside the browser process. Reader mode strips page chrome and reformats content for readability. To fetch and transform pages, the implementation exposed an HTTP endpoint bound to the loopback interface on the device.

The endpoint required no authentication. Any process able to open a socket to the local listener could submit a URL parameter. The Reader mode server then performed an authenticated fetch using Firefox's cookie jar and returned the rendered HTML to the caller.

This design broke the same-origin boundary between applications. iOS does not isolate loopback sockets between apps on the same device. An attacker-controlled app could enumerate the Reader mode port, post requests for sensitive origins, and exfiltrate the responses to a remote server.

Root Cause

The root cause is a missing authentication and authorization control on a privileged local interface. The Reader mode server trusted any local caller and proxied requests with the user's ambient browser credentials. The vulnerability falls under information exposure [CWE-200] and a broader pattern of insecure inter-process communication on mobile platforms.

Attack Vector

Exploitation requires a malicious application installed on the same iOS device as a vulnerable Firefox build. The attacking app connects to the Reader mode loopback port and issues a request specifying any target URL. Firefox processes the request with the signed-in user's cookies and returns the response. The attacker app captures the response and forwards data such as webmail content, banking session pages, or internal application data to an external endpoint. No user interaction with Firefox is required.

No public proof-of-concept code is available. Technical details are documented in Mozilla Bug Report #2036618 and Mozilla Security Advisory MFSA-2026-49.

Detection Methods for CVE-2026-8706

Indicators of Compromise

• Unexpected loopback connections from third-party applications to ports bound by Firefox for iOS
• Outbound network traffic from non-browser apps containing HTML payloads consistent with authenticated web sessions
• Installation of unvetted iOS applications on devices that also run Firefox versions prior to 151.0

Detection Strategies

• Inventory mobile endpoints to identify Firefox for iOS builds older than 151.0 through mobile device management (MDM) reporting
• Correlate App Store install events with Firefox version data to flag devices running outdated browsers alongside newly installed third-party apps
• Review iOS network extension or VPN logs for repeated loopback access patterns originating from non-Firefox processes

Monitoring Recommendations

• Track Mozilla advisory feeds for follow-up fixes to Reader mode and related local services
• Monitor mobile threat defense (MTD) telemetry for anomalous app behavior on devices used to access sensitive corporate web applications
• Audit access logs of internal web applications for session activity from iOS user agents during periods of suspected device compromise

How to Mitigate CVE-2026-8706

Immediate Actions Required

• Update Firefox for iOS to version 151.0 or later through the Apple App Store on all managed and personal devices
• Push a forced update policy through MDM for enrolled iOS devices that have Firefox installed
• Instruct users to sign out of high-value web accounts in Firefox for iOS until the update is confirmed installed

Patch Information

Mozilla addressed the issue in Firefox for iOS 151.0. The fix is described in Mozilla Security Advisory MFSA-2026-49. Apply the update from the App Store. No server-side or configuration change is required once the client is updated.

Workarounds

• Uninstall Firefox for iOS until the patched version can be installed on devices where immediate updates are not possible
• Avoid installing untrusted third-party applications on iOS devices that also run vulnerable Firefox builds
• Restrict business-critical web application access on iOS to a different browser until the update is verified

# Example MDM query to identify vulnerable Firefox for iOS installations
# Replace with the syntax supported by your MDM platform
mdm-cli devices list \
  --filter "os=iOS" \
  --app-bundle-id "org.mozilla.ios.Firefox" \
  --app-version-lt "151.0"