CVE-2026-118027 in Firefox
Summary
by MITRE • 10/27/2026
Frame poisoning in the Layout component. This vulnerability was fixed in Firefox ESR 115.44.
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Analysis
by VulDB Data Team • 10/27/2026
The discovery of frame poisoning within the Layout component of Mozilla Firefox represents a significant security concern that impacts the integrity of web content rendering and potentially allows for cross-origin data leakage or unauthorized DOM manipulation. Frame poisoning vulnerabilities typically arise when an application fails to properly validate or sanitize input before embedding it into iframe elements, allowing malicious actors to inject hostile scripts or redirect frames to untrusted domains. In the specific context of Firefox's Layout engine, this flaw suggests that under certain conditions, the browser did not adequately isolate frame contexts from their parent documents, thereby violating the principle of least privilege and enabling potential cross-site scripting (XSS) vectors or clickjacking attacks where user interactions with legitimate web pages are hijacked by malicious overlays.
From a technical perspective, such vulnerabilities often stem from improper handling of origin checks during the creation or modification of iframe elements via JavaScript APIs like document.createElement or innerHTML assignments. If the Layout component processes these dynamic changes without enforcing strict same-origin policies or sandbox attributes, an attacker could exploit this to embed content that appears legitimate but executes arbitrary code within a trusted context. This can lead to session hijacking, credential theft, or further exploitation of other browser features by gaining elevated privileges within the compromised frame environment. The vulnerability highlights critical gaps in how dynamic layout updates interact with security boundaries between different origins and sandboxed environments.
The operational impact of this flaw is substantial for users browsing untrusted websites or those exposed to sophisticated phishing campaigns that leverage iframe injection techniques. Attackers could potentially bypass content security policies if they successfully poison frames, leading to data exfiltration from sensitive web applications hosted on the same domain as the poisoned frame. Furthermore, it undermines user trust in browser-based isolation mechanisms, which are fundamental to modern web security architectures. Organizations relying on Firefox for secure browsing or internal application access face risks of unauthorized access and potential compliance violations due to inadequate protection against client-side attacks facilitated by this layout-level defect.
Mozilla addressed this issue in the release of Firefox ESR 115.44 through rigorous code audits and enhanced validation logic within the Layout component. The fix likely involved strengthening origin checks, enforcing stricter sandboxing defaults for dynamically created frames, or improving how the browser handles cross-origin resource sharing contexts during layout recalculations. Users are strongly advised to update their Firefox ESR installations immediately to mitigate these risks. Additionally, developers should ensure that any custom implementations involving iframe manipulation adhere strictly to security best practices, including setting appropriate sandbox attributes and verifying origins before embedding external content. Regular patching remains the most effective defense against such vulnerabilities as they evolve in complexity and exploitability across different browser versions.