CVE-2019-11715 in Firefox
Summary
by MITRE
Due to an error while parsing page content, it is possible for properly sanitized user input to be misinterpreted and lead to XSS hazards on web sites in certain circumstances. This vulnerability affects Firefox ESR < 60.8, Firefox < 68, and Thunderbird < 60.8.
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Analysis
by VulDB Data Team • 11/26/2025
This vulnerability represents a sophisticated cross-site scripting flaw that exploits a parsing anomaly in Mozilla's Firefox browser and Thunderbird email client. The issue stems from how the affected applications handle page content parsing, specifically when processing user input that has been properly sanitized. While the input appears safe and has undergone standard sanitization processes, the parsing mechanism fails to correctly interpret the sanitized data, creating a pathway for malicious scripts to execute within the browser context. This represents a classic case of a false positive security control where legitimate sanitization efforts inadvertently create a vulnerability due to parsing logic errors.
The technical flaw manifests in the content rendering pipeline where Firefox and Thunderbird process HTML content containing what should be harmless user input. When the parsing engine encounters specific patterns in this sanitized data, it fails to properly distinguish between legitimate content and potential malicious script payloads. This parsing error allows attackers to craft inputs that bypass standard sanitization measures, effectively transforming properly handled user data into executable code within the browser environment. The vulnerability operates at the application layer and specifically targets the HTML rendering engine's content parsing capabilities, making it particularly dangerous as it exploits the very mechanisms designed to protect against such attacks.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform a wide range of malicious activities including session hijacking, data theft, and redirection to malicious sites. Users of affected versions face significant risks when browsing websites or processing emails containing malicious payloads, as the vulnerability can be triggered through various vectors including web forms, email attachments, or embedded content. The attack surface is particularly concerning given that these applications are widely used for both web browsing and email processing, creating multiple potential entry points for exploitation. Security researchers have identified this issue as particularly dangerous because it can be exploited without requiring user interaction beyond normal browsing or email processing activities.
Mitigation strategies for this vulnerability focus primarily on immediate software updates to patched versions of Firefox ESR 60.8, Firefox 68, and Thunderbird 60.8. Organizations should prioritize deployment of these updates across all affected systems and implement comprehensive patch management processes to prevent similar issues. Network administrators should also consider implementing additional security controls such as content filtering and web application firewalls to provide defense-in-depth measures. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and follows ATT&CK technique T1211 which covers exploitation of vulnerabilities in web browsers. Security teams should also conduct thorough testing of their web applications to ensure that similar parsing issues do not exist in their own codebases, particularly in areas where user input processing and sanitization are critical components of security architecture.