CVE-2026-74934 in Firefox
Summary
by MITRE • 08/18/2026
Site isolation issue in the Graphics: CanvasWebGL component. This vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/18/2026
The identified security issue resides within the CanvasWebGL component of Mozilla Firefox, specifically concerning a failure in site isolation mechanisms. Site isolation is a critical browser security architecture designed to prevent cross-site data leakage by ensuring that resources from different origins are processed in separate processes or contexts. When this mechanism fails, it creates an environment where malicious websites may potentially access sensitive information belonging to other sites loaded within the same browser instance. This vulnerability represents a significant deviation from expected sandboxing behaviors, undermining one of the primary defenses against cross-site scripting and data exfiltration attacks that rely on breaking out of origin boundaries.
From a technical perspective, the flaw likely involves improper handling of WebGL contexts or memory allocation strategies that allow for unintended sharing of state between different origins. In modern web browsers, WebGL operations are often sandboxed to prevent access to system resources such as GPU drivers and textures beyond what is explicitly permitted by the current document's origin. A breakdown in this isolation could permit a malicious script running under one domain to read or manipulate data associated with another domain’s canvas context. This type of vulnerability falls squarely within the CWE-200 category, which covers Information Exposure, particularly when it leads to unauthorized access to sensitive information through side channels or memory corruption techniques that bypass standard permission checks.
The operational impact of this vulnerability is substantial for users who engage in activities requiring high levels of privacy and security, such as online banking, accessing corporate intranets, or managing personal accounts on multiple platforms simultaneously. An attacker could craft a malicious webpage designed to exploit the CanvasWebGL flaw to extract data from other tabs or windows that are open but not actively viewed by the user. This capability effectively neutralizes the browser’s ability to contain threats within their respective origins, potentially leading to session hijacking, credential theft, or unauthorized access to protected resources. The risk is exacerbated in environments where users frequently switch between trusted and untrusted sites without closing tabs, as the isolation boundary becomes porous due to this specific implementation error.
To mitigate these risks, it is imperative that all affected versions of Firefox are updated immediately. The vulnerability has been addressed in Firefox version 154, which includes patches for the underlying CanvasWebGL logic to enforce stricter separation between origins. Additionally, users relying on extended support releases must ensure they have applied updates corresponding to Firefox ESR 115.39, Firefox ESR 140.14, and Firefox ESR 153.1. These patches likely involve enhancements to the rendering engine’s security checks, ensuring that WebGL contexts are correctly isolated at both the process level and the JavaScript execution context level. Organizations should prioritize patching their browser fleets to maintain compliance with modern web security standards and reduce the attack surface associated with cross-origin data leakage.
This incident aligns with known threat actor tactics described in the MITRE ATT&CK framework, specifically those related to collection via client-side scripting or exploitation of software vulnerabilities for initial access and lateral movement within a user’s session. By addressing this flaw, Mozilla reinforces its commitment to maintaining robust security boundaries that protect users from sophisticated web-based attacks. Continued vigilance regarding browser updates remains essential, as such isolation failures can be leveraged in targeted campaigns aiming to compromise sensitive user data through seemingly benign WebGL interactions on compromised or malicious websites.