Description

Site isolation issue in the Graphics: WebRender component. This vulnerability was fixed in Firefox 154 and Firefox ESR 153.1.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.4",
  "pubDate": "2026-08-18T13:17:34.190Z",
  "pubdate": "2026-08-18T13:17:34.190Z",
  "executiveSummary": "A critical site isolation vulnerability has been identified within the Graphics: WebRender component of the Firefox browser ecosystem. This security flaw compromises the browser's security boundary enforcement, specifically undermining site isolation mechanisms designed to separate content from different origins into distinct operating system processes. The primary impact of this vulnerability involves the potential bypass of same-origin policy protections and process isolation boundaries, which could allow a malicious web site or compromised rendering process to access sensitive data belonging to other origins loaded within the browser context. The affected systems include Firefox prior to version 154 and Firefox ESR prior to version 153.1. The risk implications are severe, as successful exploitation could lead to cross-site data leakage, unauthorized information disclosure, and potential compromise of user privacy and session integrity. Attacker capabilities typically require coercing a user into navigating to a maliciously crafted web page designed to trigger the isolation failure within the rendering engine. Exploitation requirements generally entail the execution of untrusted web content within the browser environment, leveraging specific flaws in how WebRender handles process boundaries and cross-origin resource sharing or memory separation.",
  "technicalDetails": "The vulnerability resides in the Graphics: WebRender component, which is responsible for modern GPU-accelerated rendering in the Firefox browser. Site isolation is a core architectural defense-in-depth mechanism implemented to ensure that pages from different websites are loaded in separate operating system processes, thereby mitigating Spectre-style side-channel attacks and preventing unauthorized cross-origin data access. The root cause stems from a flaw in how the WebRender component enforces these process boundaries, leading to a failure in maintaining strict isolation between distinct origin contexts. During execution, the vulnerable component mishandles inter-process communication, memory management, or rendering state synchronization across process boundaries. Affected versions include Firefox prior to version 154 and Firefox ESR prior to version 153.1. Authentication and privilege requirements for exploitation are minimal from the perspective of the attacker; an adversary does not need prior administrative access or local system privileges. Instead, the attack vector relies on network exposure via malicious web content delivered over standard web protocols. The attack flow begins when a user navigates to a malicious URL controlled by the attacker. The malicious page loads and interacts with the rendering engine, specifically targeting the WebRender component to exploit the site isolation bypass. By triggering the flaw, the attacker circumvents process separation controls, enabling the malicious rendering context to inspect memory structures or cache states associated with other origins processed by the browser. Post-exploitation impact includes the potential extraction of sensitive cross-origin data, such as authentication tokens, personal identifiable information, or session secrets, depending on what information resides within the shared or improperly isolated memory spaces managed by the graphics subsystem."
}