CVE-2026-117990 in Firefox
Summary
by MITRE • 10/27/2026
Sandbox escape due to incorrect boundary conditions in the Graphics: WebRender component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified security flaw resides within the WebRender subsystem of Mozilla Firefox, a critical rendering engine responsible for translating web content into visual output on the user's display. Specifically, the issue stems from incorrect boundary condition handling during memory access operations. In complex graphics processing scenarios, particularly those involving WebGL or advanced CSS animations, the renderer must strictly adhere to allocated buffer limits and coordinate spaces. When these boundaries are not correctly validated before data is read or written, it creates a scenario where an attacker can manipulate input parameters to cause the application to access memory locations outside of its intended scope. This type of error is classically categorized under CWE-125 Out-of-bounds Read or CWE-787 Out-of-bounds Write depending on whether the exploit involves reading sensitive data from adjacent memory regions or overwriting critical control structures and variables within the process space.
From an operational perspective, this vulnerability poses a severe risk to user security because it facilitates sandbox escape. The browser's multi-process architecture relies heavily on strict isolation between different tabs and origins to prevent malicious websites from affecting other parts of the system or accessing sensitive local resources. By exploiting incorrect boundary conditions in WebRender, a remote attacker can potentially break out of this restricted execution environment. Once the sandbox barrier is breached, the attacker gains the ability to execute arbitrary code with the privileges of the current user. This escalation allows for unauthorized access to personal files, session cookies, and other sensitive data stored locally on the victim's machine. Furthermore, it enables the installation of persistent malware or the use of the compromised system as a pivot point for further network attacks, significantly expanding the blast radius beyond the browser itself.
The technical mechanism likely involves crafting specific graphical elements that trigger edge cases in the rendering pipeline where index calculations fail to account for maximum array sizes or coordinate limits. When these malformed inputs are processed by WebRender, they lead to memory corruption or unauthorized data leakage. This aligns with MITRE ATT&CK techniques related to Defense Evasion and Privilege Escalation, specifically those involving exploitation of client-side software vulnerabilities such as CWE-120 Buffer Copy without Checking Size of Input. The attacker would typically deliver the malicious content through a compromised website or a phishing campaign that directs the victim to render the exploit code within an iframe or directly in the browser window.
To mitigate this risk, users must ensure they are running Firefox version 159 or later, as well as any supported Extended Support Release (ESR) versions including 153.6 and newer patches. These updates contain the necessary logic corrections to enforce strict boundary checks within the WebRender component. Organizations should prioritize patch management cycles to deploy these fixes across all endpoints promptly. Additionally, implementing application whitelisting or restricting script execution in untrusted zones can provide an additional layer of defense against exploitation attempts that rely on triggering such rendering engine flaws. Regular security awareness training for users regarding suspicious links and websites remains a vital complementary control to reduce the likelihood of initial compromise leading up to this technical vulnerability being triggered.