CVE-2019-9797 in Firefox
Summary
by MITRE
Cross-origin images can be read in violation of the same-origin policy by exporting an image after using createImageBitmap to read the image and then rendering the resulting bitmap image within a canvas element. This vulnerability affects Firefox < 66.
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Analysis
by VulDB Data Team • 08/09/2025
This vulnerability represents a significant bypass of web browser security mechanisms that violates the fundamental same-origin policy enforcement. The flaw exists in the Firefox browser's handling of cross-origin image data when specific API operations are performed in sequence. The vulnerability specifically affects Firefox versions prior to 66, where the security boundary between different origins is improperly maintained during image processing operations. The same-origin policy serves as a cornerstone of web security by preventing malicious scripts from accessing data from different origins without proper authorization, and this bypass undermines that critical protection.
The technical mechanism behind this vulnerability involves the interaction between createImageBitmap API and canvas rendering operations. When a web application uses createImageBitmap to process cross-origin images, the resulting bitmap data can be subsequently rendered within a canvas element in a manner that exposes pixel-level information from the original cross-origin resource. This occurs because the browser's internal handling of these operations does not properly enforce origin restrictions during the bitmap processing phase. The vulnerability exploits a gap in the security model where data flows from one security context to another without proper validation of cross-origin boundaries. This type of flaw falls under the category of information disclosure vulnerabilities and can be classified as CWE-200 (Information Exposure) with potential implications for data leakage across origin boundaries.
The operational impact of this vulnerability extends beyond simple data exposure to potentially enable sophisticated attacks such as cross-origin data exfiltration and fingerprinting. Attackers could leverage this vulnerability to extract sensitive information from images hosted on different origins, potentially including embedded metadata, visual patterns, or other data that should remain protected by the same-origin policy. The attack vector becomes particularly concerning when considering that createImageBitmap is commonly used in web applications for image manipulation and processing, making this vulnerability exploitable in a wide range of legitimate web applications. This flaw can be categorized under ATT&CK technique T1071.001 (Application Layer Protocol: Web Protocols) and potentially T1566 (Phishing) when combined with other attack vectors that exploit browser security gaps. The vulnerability demonstrates how seemingly innocuous API operations can create security risks when combined in specific sequences, highlighting the complexity of modern web security implementations.
Mitigation strategies for this vulnerability require immediate browser updates to versions 66 or later where the security fix has been implemented. Organizations should ensure their Firefox installations are current and regularly updated to prevent exploitation of this and similar vulnerabilities. Additionally, developers should be aware of the potential risks when using createImageBitmap with cross-origin resources and implement proper security controls in their applications. The fix likely involves strengthening the origin validation checks during bitmap processing operations and ensuring that cross-origin data cannot be accessed through canvas rendering operations that might expose pixel-level information from restricted resources. This vulnerability underscores the importance of comprehensive security testing of web APIs and the need for continuous monitoring of browser security updates to maintain robust web application security postures.