CVE-2026-74974 in Firefox
Summary
by MITRE • 08/18/2026
Same-origin policy bypass in the Graphics: ImageLib 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 • 08/21/2026
The identified vulnerability represents a critical failure in the enforcement of the Same-Origin Policy within Mozilla's ImageLib component, specifically affecting how image resources are handled during cross-origin requests. The Same-Origin Policy is a fundamental security mechanism implemented by web browsers to restrict how a document or script loaded from one origin can interact with resources from another origin. This isolation prevents malicious scripts on one page from obtaining access to sensitive data on another page through the Document Object Model, thereby mitigating risks such as cross-site scripting and data theft. In this specific instance, the flaw lies in the graphics subsystem's handling of image decoding and caching mechanisms, where improper validation or state management allows an attacker to bypass these restrictions under certain conditions.
Technically, the vulnerability stems from a logic error within the ImageLib module that processes various image formats such as PNG, JPEG, GIF, and WebP. When a webpage attempts to load an image resource hosted on a different domain than the script executing it, the browser is supposed to enforce strict origin checks before allowing any manipulation of the image data via JavaScript APIs like getImageData or canvas operations. However, due to race conditions or improper state tracking in the asynchronous decoding pipeline, the application may expose pixel data from cross-origin images without triggering the expected security exceptions. This bypass occurs because the internal cache or decoder does not correctly associate the loaded resource with its originating context before making it available for script access, effectively treating a restricted resource as if it were same-origin.
The operational impact of this vulnerability is significant for users browsing untrusted web content. An attacker could craft a malicious webpage that loads an image from a victim's bank or email provider and then reads the pixel data to extract sensitive information such as login credentials displayed in CAPTCHAs, session tokens embedded in images, or private user data rendered visually on the page. This capability undermines the core trust model of web browsers, allowing for sophisticated phishing attacks where visual elements are harvested programmatically rather than through traditional form injection techniques. The severity is further amplified by the ubiquity of image loading in modern web applications and the potential for automated scraping of sensitive graphical content that was previously considered safe from script-based extraction.
Mitigation strategies primarily involve applying the vendor-provided patches released to address this flaw immediately across all affected environments. For enterprise deployments, it is essential to ensure that Firefox versions 154, ESR 115.39, ESR 140.14, and ESR 153.1 are deployed consistently across all client machines. In addition to patching, organizations should implement Content Security Policy headers with strict directives regarding image loading and script execution to add a layer of defense-in-depth. Monitoring browser console logs for unexpected cross-origin errors can also help in detecting potential exploitation attempts in real-time. Furthermore, user education remains vital, as awareness of social engineering tactics that leverage visual data theft complements technical controls.
From a classification perspective, this vulnerability aligns with CWE-200, which covers Exposure of Sensitive Information to an Unauthorized Actor, and specifically relates to improper enforcement of security policies regarding resource access boundaries. In the context of the MITRE ATT&CK framework, this flaw facilitates techniques associated with Collection via Browser Exfiltration, where attackers harvest data directly from a user's browser environment by exploiting trust relationships between different origins. The successful exploitation relies on the attacker hosting malicious content that tricks users into loading resources from trusted but sensitive domains, leveraging the browser's own rendering engine to bypass security boundaries. Addressing this issue requires not only software updates but also rigorous auditing of web application practices to ensure they do inadvertently rely on implicit trust assumptions about image handling mechanisms.