CVE-2026-13356 in Firefox for iOS
Summary
by MITRE • 07/07/2026
A malicious webpage could interrupt a pending navigation by enqueuing a synchronous JavaScript dialog, causing the browser UI to display the destination origin in the address bar while continuing to render attacker-controlled content. This vulnerability was fixed in Firefox for iOS 152.3.
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Analysis
by VulDB Data Team • 07/07/2026
This vulnerability represents a sophisticated browser security flaw that exploits the timing and execution flow of web navigation processes within mobile browser environments. The issue occurs when a malicious webpage attempts to manipulate the browser's navigation state by inserting synchronous JavaScript dialogs into the execution queue during an ongoing navigation event. This creates a misleading user interface scenario where the browser address bar displays the intended destination URL while simultaneously rendering content from the attacking domain, effectively creating a deceptive browsing experience that could mislead users about their actual location.
The technical mechanism behind this vulnerability involves the interaction between the browser's navigation handling system and JavaScript execution queues. When a navigation is in progress, the browser maintains a pending state where it processes various events and scripts. A malicious actor can exploit this window by executing synchronous dialog functions such as alert() or confirm() calls that block the JavaScript execution thread. This blocking behavior causes the browser UI to update the address bar with the target origin while the attacker's content continues rendering in the main document context, bypassing normal security boundaries that should prevent such cross-origin content rendering.
The operational impact of this vulnerability extends beyond simple user confusion to potentially enable more serious attacks such as phishing schemes and credential theft. Users may be deceived into believing they are navigating to a legitimate destination while unknowingly interacting with malicious content that can capture sensitive information or perform unauthorized actions. The vulnerability specifically affects mobile browser environments where the UI rendering and navigation handling processes differ from desktop implementations, making it particularly concerning for mobile security. This type of attack aligns with tactics described in the attack pattern taxonomy under the category of user interface deception and session hijacking.
This vulnerability is classified as a variant of input validation and user interface manipulation issues, relating to CWE-691 which covers inadequate input validation and CWE-1241 which addresses improper handling of UI state changes. The flaw demonstrates weaknesses in how browsers manage navigation state transitions and the synchronization between different execution contexts during page loading processes. Security researchers have noted that mobile browser implementations often have distinct timing characteristics that can create additional attack surfaces not present in desktop environments, making such vulnerabilities particularly dangerous in mobile contexts where users may be less vigilant about security warnings.
The mitigation for this vulnerability requires comprehensive updates to browser rendering engines and navigation handling protocols. Firefox for iOS version 152.3 addressed the issue by implementing stricter controls over JavaScript execution during navigation events and by ensuring that UI state updates cannot be manipulated through synchronous dialog injection techniques. Security best practices recommend regular browser updates, implementation of content security policies, and user education about recognizing potential phishing attempts. Organizations should also consider deploying additional security layers such as web application firewalls and network monitoring solutions to detect anomalous navigation patterns that might indicate exploitation attempts.
The fix implemented by Mozilla demonstrates the importance of maintaining consistent security boundaries across different execution contexts within browser environments. Modern browser security architectures must account for the complex interactions between asynchronous and synchronous JavaScript execution, navigation state management, and user interface updates. This vulnerability highlights the need for comprehensive testing of edge cases in browser implementations, particularly focusing on timing-sensitive operations that can create security artifacts during state transitions. The remediation approach typically involves implementing more robust queue management systems that prevent unauthorized manipulation of navigation events while maintaining legitimate user interaction capabilities.
This type of vulnerability represents a growing concern in mobile security environments where the attack surface is expanded by the convergence of multiple execution contexts and UI rendering processes. The fix required careful consideration of backward compatibility issues while ensuring that legitimate browser functionality remains intact. Security professionals should monitor similar vulnerabilities across different browser vendors as they often share common architectural patterns that can lead to similar weaknesses. The incident underscores the critical importance of continuous security assessment and rapid response capabilities in maintaining browser security standards, particularly for mobile platforms where users may have fewer security controls available compared to desktop environments.