CVE-2026-81267 in Firefox for iOS
Summary
by MITRE • 08/31/2026
A malicious webpage could stall a popup's cross-origin navigation after commit, causing the address bar to display the destination origin while continuing to render attacker-controlled content. This vulnerability was fixed in Firefox for iOS 155.0.
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Analysis
by VulDB Data Team • 08/31/2026
The described vulnerability represents a sophisticated user interface spoofing attack vector that exploits the separation between browser state management and rendering logic within mobile web browsers, specifically affecting Firefox for iOS prior to version 155.0. This flaw allows an attacker-controlled webpage to manipulate the navigation lifecycle of cross-origin popups in a manner that creates a deceptive visual environment for the end user. By stalling the actual commit phase of a popup's cross-origin navigation while allowing the address bar to update with the destination origin, the browser inadvertently presents a false sense of security and legitimacy. This discrepancy between the displayed URL and the rendered content is a classic indicator of UI redressing attacks, where the goal is to trick users into interacting with malicious elements under the guise of a trusted or expected domain.
From a technical perspective, this issue stems from an improper synchronization mechanism within the browser's navigation stack and rendering engine. When a cross-origin popup initiates navigation, the browser typically updates the user interface components such as the address bar to reflect the new target origin before fully committing the load in the background process. In this specific case, the commit operation was successfully stalled or delayed by malicious code execution on the source page, yet the UI update proceeded without waiting for the content validation and loading completion. This race condition enables a state where the user sees one thing (the trusted destination URL) while experiencing another (attacker-controlled HTML, CSS, and JavaScript). Such behavior undermines the fundamental trust model of web browsers, which relies on the address bar as the primary indicator of identity and security context for the current document being displayed.
The operational impact of this vulnerability is significant in terms of social engineering potential. Attackers can leverage this UI spoofing technique to create phishing pages that appear to be hosted on legitimate domains or trusted services. For instance, an attacker could craft a scenario where clicking a link opens a popup intended for a banking site, but due to the stall, the address bar shows the bank's URL while rendering a fake login form controlled by the attacker. Users are more likely to enter sensitive credentials when they perceive the context as legitimate based on the visible URL. This type of attack bypasses traditional security warnings that rely on certificate validation or domain matching because the visual representation aligns with expectations, even though the underlying content is malicious. It effectively neutralizes one of the primary defenses against phishing: user awareness of the current website's identity.
This vulnerability maps directly to CWE-1021 Improper Restriction of Rendered UI Layers or Frames and CWE-847 Information Exposure Through an Error Message if considered in terms of state leakage, but more accurately aligns with CWE-695 Use of Low-Level Functions that Allow for Production of Uncontrolled Memory Access if viewed through the lens of implementation flaws leading to inconsistent states. In the context of the MITRE ATT&CK framework, this behavior is categorized under T1082 Software Discovery or more specifically within the broader category of UI Redressing (T1653) and Phishing via Malicious Links (T1566). The attack vector relies on social engineering combined with technical exploitation to deceive users into performing actions they would not otherwise perform, such as submitting credentials or downloading malware.
Mitigation for this vulnerability primarily involves the software update provided by Mozilla in Firefox for iOS version 155.0, which corrects the synchronization logic between navigation commits and UI updates. For organizations deploying mobile browsers at scale, it is critical to ensure that all client devices are updated to patched versions immediately upon release of security advisories. Additionally, users should be educated about verifying content integrity beyond just the URL bar, such as checking for secure connection indicators like padlock icons or validating certificate details manually when dealing with sensitive transactions. Browser vendors continue to harden these navigation flows by implementing stricter checks that prevent UI updates from proceeding until the underlying document load is fully verified and committed, thereby closing the window of opportunity for such race condition exploits.