CVE-2019-11718 in Firefox
Summary
by MITRE
Activity Stream can display content from sent from the Snippet Service website. This content is written to innerHTML on the Activity Stream page without sanitization, allowing for a potential access to other information available to the Activity Stream, such as browsing history, if the Snipper Service were compromised. This vulnerability affects Firefox < 68.
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Analysis
by VulDB Data Team • 07/10/2020
The vulnerability described in CVE-2019-11718 represents a critical cross-site scripting risk within the Firefox browser's Activity Stream feature, which serves as a personalized dashboard displaying browsing history, bookmarks, and recommended content. This flaw exists in the way Firefox handles content integration from external sources, specifically the Snippet Service website that provides dynamic content to enhance the user experience. The vulnerability arises from the browser's failure to properly sanitize data received from this external service before rendering it within the Activity Stream interface, creating a potential attack vector that could compromise user privacy and system security.
The technical implementation of this vulnerability stems from the improper handling of HTML content through the innerHTML property, which is a common pattern in web development but becomes dangerous when used with untrusted data sources. When Firefox processes content from the Snippet Service, it directly writes this data into the Activity Stream page using innerHTML without adequate sanitization or validation, allowing malicious content to execute within the context of the user's browsing session. This approach violates fundamental security principles for handling external content and creates an environment where attackers can inject scripts or manipulate the DOM structure to access sensitive information.
The operational impact of this vulnerability extends beyond simple XSS attacks, as it provides potential attackers with access to sensitive user data that the Activity Stream component can already access. Since the Activity Stream page operates with elevated privileges and can access browsing history, bookmarks, and other personal data, a successful exploitation could allow an attacker to extract this information even when the Snippet Service is compromised. This represents a privilege escalation scenario where an attacker can leverage a relatively simple injection point to access data that should normally be protected by browser security boundaries, effectively creating a backdoor into the user's browsing context.
The vulnerability affects Firefox versions prior to 68, indicating that this was a known issue that required a specific version update to remediate. Organizations and users should have been immediately concerned about this exposure, particularly in environments where Firefox was the primary browser and where users engaged with potentially untrusted websites. The risk is compounded by the fact that the Snippet Service could be compromised through various attack vectors, including supply chain attacks, phishing, or other methods that might allow attackers to inject malicious content into the service. This vulnerability aligns with CWE-79, which describes cross-site scripting flaws, and represents a classic case of inadequate input validation and output encoding in web applications.
Security mitigations for this vulnerability include immediate browser updates to Firefox 68 or later versions where the sanitization issues have been addressed through proper HTML escaping and content validation. Organizations should also implement network monitoring to detect potential exploitation attempts, as well as educate users about the importance of keeping their browsers updated. The fix typically involves implementing proper input sanitization before rendering external content, using secure coding practices such as DOMPurify or similar libraries, and ensuring that all external content is properly validated and escaped before insertion into the DOM. This vulnerability demonstrates the critical importance of maintaining secure coding practices in browser components that handle external content, as these features often operate with elevated privileges and can become attack vectors for more serious security breaches.