Description

Privilege escalation due to use-after-free in the Graphics: WebRender component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-09-29T13:17:44.760Z",
  "pubdate": "2026-09-29T13:17:44.760Z",
  "executiveSummary": "This vulnerability is a critical use-after-free defect located within the Graphics: WebRender component of the Mozilla Firefox browser engine.\nA use-after-free condition occurs when memory is accessed after it has been explicitly deallocated, leading to undefined behavior, potential memory corruption, or arbitrary code execution.\nThe vulnerability allows a malicious actor to achieve privilege escalation, potentially breaking out of the content process sandbox.\nAffected products include Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.\nSuccessful exploitation could allow an attacker to execute arbitrary code within the context of the application, resulting in full system compromise or unauthorized access to sensitive user data.\nThe flaw necessitates specific memory manipulation patterns, typically delivered via crafted web content that interacts with the GPU-accelerated rendering pipeline.\nGiven the nature of use-after-free vulnerabilities, the risk is severe, requiring immediate application of security patches to mitigate the threat of remote code execution.",
  "technicalDetails": "The vulnerability originates within the WebRender component, which is responsible for hardware-accelerated rendering of web content in Firefox.\nThe root cause is a use-after-free (UAF) flaw resulting from improper lifecycle management of graphics objects within the rendering pipeline.\nIn a UAF scenario, an object is freed from memory while a dangling pointer persists elsewhere in the application. If the engine performs a subsequent operation using this dangling pointer, it accesses memory that may have been repurposed for other objects or data structures.\nExploitation involves heap grooming or spraying techniques to influence the state of the heap memory. By forcing the browser to allocate a controlled object into the memory slot previously occupied by the freed object, the attacker gains the ability to manipulate the application's internal data structures, function pointers, or virtual method tables.\nThe attack flow generally commences with the rendering of a maliciously crafted document or web page designed to trigger specific GPU command sequences. These sequences interact with the WebRender interface to force an untimely deallocation of an internal graphics resource.\nOnce the resource is freed, the attacker utilizes auxiliary heap operations to occupy that memory region with malicious payload data. When the browser engine subsequently attempts to reference the original object pointer, it instead executes or operates upon the attacker-controlled data.\nThis behavior can lead to control-flow hijacking, where the attacker redirects the instruction pointer to arbitrary memory addresses, such as a ROP (Return-Oriented Programming) chain or a shellcode buffer.\nBecause the Graphics: WebRender component operates with significant privileges within the rendering architecture, successful exploitation effectively bypasses standard browser-level protections, enabling the attacker to escalate privileges and compromise the integrity of the underlying host operating system process.\nThe vulnerability affects multiple versions of Firefox, including 157, ESR 153.4, ESR 115.42, and ESR 140.17, necessitating updates to address the underlying memory safety violation.\nThe exposure is widespread for any user accessing untrusted web content, as the trigger mechanism resides within the core rendering logic, which is exercised during standard navigation and DOM manipulation."
}