CVE-2016-1941 in Firefox
Summary
by MITRE
The file-download dialog in Mozilla Firefox before 44.0 on OS X enables a certain button too quickly, which allows remote attackers to conduct clickjacking attacks via a crafted web site that triggers a single-click action in a situation where a double-click action was intended.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/06/2022
The vulnerability described in CVE-2016-1941 represents a sophisticated clickjacking flaw that specifically targets the file download dialog interface in Mozilla Firefox versions prior to 44.0 on macOS operating systems. This security weakness stems from an improper timing mechanism within the user interface components that control how download dialogs respond to user interactions. The flaw manifests when the system enables a critical button in the file download dialog before the user has had sufficient time to complete their intended double-click action, creating a window of opportunity for malicious actors to exploit this temporal inconsistency.
The technical implementation of this vulnerability involves the asynchronous handling of user interface events within Firefox's download dialog subsystem. When a web page triggers a file download request, the browser's interface must properly sequence the display of various interactive elements including confirmation buttons. In vulnerable versions, the system prematurely enables a button that should typically require a double-click interaction, allowing attackers to craft malicious web pages that automatically trigger single-click actions. This timing discrepancy creates a race condition where the malicious site can manipulate the user interface to execute unintended actions that would normally require deliberate double-click input from the user.
From an operational perspective, this vulnerability enables remote attackers to conduct sophisticated clickjacking attacks that can potentially lead to unauthorized file downloads or system compromises. The attack vector specifically exploits the difference between single-click and double-click behaviors in the macOS file system dialog interface, where a single-click might initiate a download while a double-click would typically open a confirmation dialog. Attackers can craft web pages that appear benign but actually trigger automated actions within the download dialog, potentially downloading malicious files or executing unintended operations without user awareness. The vulnerability is particularly concerning because it operates at the user interface level, making it difficult to detect through traditional network-based security measures and relying instead on social engineering elements that trick users into performing unintended actions.
The security implications of CVE-2016-1941 align with common attack patterns documented in the attack tactics and techniques framework, specifically relating to user interaction manipulation and session hijacking approaches. This vulnerability demonstrates how seemingly minor interface timing issues can create significant security risks, particularly when they involve user confirmation mechanisms that are designed to prevent accidental actions. The flaw essentially undermines the intended user experience design where double-click actions are typically reserved for more critical operations that require explicit user confirmation, while single-click actions are meant for less sensitive operations. This represents a violation of the principle of least privilege in user interface design, where the system should not allow potentially dangerous actions to be triggered by accidental or automated interactions.
Organizations and users affected by this vulnerability should immediately update to Firefox version 44.0 or later, which includes the necessary patches to address the timing issue in the download dialog interface. The fix implemented by Mozilla addresses the underlying race condition by properly synchronizing the button enablement timing with the expected user interaction patterns. Additional mitigations include implementing browser security policies that restrict automatic download behavior, using security extensions that monitor for suspicious download dialog interactions, and conducting user awareness training to recognize potentially malicious download prompts. Security teams should also monitor for exploitation attempts that might involve crafting web pages specifically designed to trigger this vulnerability, as the attack requires no special privileges or complex exploitation techniques beyond the ability to host malicious web content. This vulnerability serves as a reminder of the critical importance of proper user interface timing and event handling in security-sensitive applications, particularly those that involve user confirmation mechanisms and file system operations.