CVE-2026-74978 in Firefox
Summary
by MITRE • 08/18/2026
Clickjacking issue in the Widget component. This vulnerability was fixed in Firefox 154 and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/20/2026
The identified Clickjacking vulnerability within the Widget component represents a significant user interface manipulation risk that exploits the browser's rendering engine to deceive end users into interacting with hidden or obscured elements. This class of attack, formally categorized under CWE-1021 as Improper Restriction of Rendered UI Layers, relies on the ability of an attacker to embed a legitimate web page within an invisible iframe and overlay it with transparent layers containing malicious controls. When a user interacts with what they perceive to be benign content from the trusted domain, their clicks are inadvertently directed toward hidden interactive elements such as buttons or links controlled by the attacker. This mechanism effectively bypasses standard authentication checks because the browser treats the action as if it were initiated directly on the target site, leveraging the victim's existing session privileges without requiring additional credentials or social engineering beyond visual deception.
The technical flaw stems from insufficient enforcement of frame-busting techniques and inadequate implementation of Content Security Policy directives specifically targeting framing behaviors within the Widget component. In many web applications, developers fail to implement X-Frame-Options headers set to DENY or SAMEORIGIN, or neglect to use JavaScript-based checks that detect if the page is being loaded inside an iframe from a different origin. The absence of these protective measures allows external domains to load the vulnerable widget in a frame with zero opacity and positioned precisely over critical interface elements. This misconfiguration enables cross-origin framing attacks where the visual presentation does not match the underlying functional reality, leading users to perform actions such as changing account settings, transferring funds, or executing administrative commands without their explicit consent or awareness of the true target of their interaction.
The operational impact of this vulnerability is severe, particularly in applications handling sensitive user data or financial transactions. Successful exploitation can lead to unauthorized state changes within the application, allowing attackers to modify user profiles, initiate money transfers, or alter security settings such as two-factor authentication configurations. Because Clickjacking attacks are visually indistinguishable from legitimate interactions for many users, especially on mobile devices where touch targets may overlap significantly, the rate of successful exploitation is high. Furthermore, this vulnerability can serve as a precursor to more complex attack chains, including account takeover and data exfiltration, thereby compromising the integrity and confidentiality of user accounts associated with the affected service. The trust relationship between the user and the application is fundamentally undermined when users cannot reliably distinguish between intended actions and those coerced through UI redressing techniques.
Mitigation strategies must focus on both server-side header enforcement and client-side defensive coding practices to fully neutralize this threat vector. Implementing strict Content Security Policy (CSP) directives, specifically frame-ancestors set to 'self' or specific trusted domains, provides a robust defense by instructing compliant browsers to refuse loading the page in any foreign iframe context. Additionally, setting the X-Frame-Options header to DENY ensures legacy browser compatibility while maintaining strong protection against framing attacks. On the client side, developers should implement JavaScript-based frame-busting scripts that detect if the window is being framed and immediately break out of the container by redirecting the top-level window or displaying an error message. Regular security audits and automated scanning for UI redressing vulnerabilities are essential to identify such misconfigurations early in the development lifecycle. The resolution included in Firefox 154 and Firefox ESR 153.1 addresses these implementation gaps within the browser's handling of widget components, reinforcing best practices for rendering isolation and frame permission checks to prevent unauthorized framing scenarios.