CVE-2026-81267 Overview
CVE-2026-81267 is an address bar spoofing vulnerability in Mozilla Firefox for iOS. A malicious webpage can stall a popup's cross-origin navigation after commit. The address bar displays the destination origin while the page continues to render attacker-controlled content. This mismatch enables convincing phishing scenarios because users see a trusted origin in the URL bar. The issue is classified under [CWE-451: User Interface (UI) Misrepresentation of Critical Information]. Mozilla fixed the flaw in Firefox for iOS 155.0 and tracked it through advisory MFSA-2026-81.
Critical Impact
Attackers can display a legitimate origin in the Firefox iOS address bar while rendering arbitrary content, enabling high-fidelity phishing against mobile users.
Affected Products
- Mozilla Firefox for iOS versions prior to 155.0
- iPhone OS builds of mozilla:firefox_mobile
- Any iOS device running a vulnerable Firefox build
Discovery Timeline
- 2026-08-31 - CVE-2026-81267 published to NVD
- 2026-09-03 - Last updated in NVD database
Technical Details for CVE-2026-81267
Vulnerability Analysis
The flaw involves a race between navigation commit and rendering in popup windows on Firefox for iOS. When a script-controlled popup initiates a cross-origin navigation, the browser commits the new origin and updates the address bar. If the attacker stalls the subsequent load, the previous document remains visible while the URL bar advertises the new origin.
The result is a UI misrepresentation issue where the security indicator no longer reflects the rendered content. Users relying on the address bar to validate the site they are viewing receive false assurance. Attackers can craft popups that display banking, corporate SSO, or webmail origins while rendering credential-harvesting forms.
Exploitation requires user interaction, specifically triggering the popup and viewing the spoofed content. The scope is limited to information integrity of the browser chrome rather than code execution or memory corruption.
Root Cause
The root cause is improper synchronization between the navigation state machine and the rendering pipeline. Firefox for iOS updates the address bar upon navigation commit but does not enforce that the destination document has replaced the previous frame content before the URL indicator changes. An attacker who deliberately stalls the network response or navigation completion holds the UI in an inconsistent state.
Attack Vector
Exploitation is remote and requires a victim to visit an attacker-controlled page that opens a popup. The malicious page programmatically navigates the popup to a target origin, then delays the response. The victim sees the destination origin in the address bar while interacting with content served by the attacker. No authentication or elevated privileges are required.
Verified proof-of-concept code is not publicly available. See Mozilla Bug Report #2052758 for technical details from the vendor.
Detection Methods for CVE-2026-81267
Indicators of Compromise
- Firefox for iOS installations reporting versions below 155.0 in mobile device management (MDM) inventories
- User reports of popup windows displaying a familiar origin while showing unexpected login prompts
- Web proxy logs showing long-stalled HTTP responses to popup navigations from mobile Firefox user agents
Detection Strategies
- Inventory managed iOS devices for Firefox versions and flag any build earlier than 155.0
- Correlate phishing report tickets with mobile Firefox user-agent strings in email and web gateway telemetry
- Monitor authentication logs for credential submissions from iOS Firefox sessions that lack expected referrer patterns
Monitoring Recommendations
- Ingest mobile browser version telemetry into your SIEM to identify unpatched endpoints
- Track outbound connections from mobile devices to newly registered domains commonly used in phishing kits
- Alert on authentication anomalies from mobile clients targeting high-value SaaS applications
How to Mitigate CVE-2026-81267
Immediate Actions Required
- Update Firefox for iOS to version 155.0 or later through the Apple App Store on all managed and personal devices
- Push a mandatory app update policy via MDM for enterprise-managed iPhones and iPads
- Notify users through security awareness channels to verify the URL bar and page content together, not in isolation
Patch Information
Mozilla addressed CVE-2026-81267 in Firefox for iOS 155.0. Details are published in the Mozilla Security Advisory MFSA-2026-81. Apply the update via the App Store or enterprise MDM deployment.
Workarounds
- Instruct users to close popup windows immediately if content does not load within a normal timeframe
- Restrict use of Firefox for iOS on managed devices until version 155.0 is confirmed installed
- Enforce phishing-resistant authentication such as FIDO2 or platform passkeys so that spoofed origins cannot harvest reusable credentials
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
