CVE-2017-7750 in Firefox
Summary
by MITRE
A use-after-free vulnerability during video control operations when a "<track>" element holds a reference to an older window if that window has been replaced in the DOM. This results in a potentially exploitable crash. This vulnerability affects Firefox < 54, Firefox ESR < 52.2, and Thunderbird < 52.2.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability described in CVE-2017-7750 represents a critical use-after-free condition that occurs within the Mozilla Firefox browser and Thunderbird email client. This flaw manifests during video control operations when processing "<track>" elements in html documents, specifically when these elements maintain references to windows that have been subsequently removed or replaced within the Document Object Model. The technical nature of this vulnerability stems from improper memory management practices where the browser fails to properly invalidate references to destroyed window objects, creating a scenario where freed memory can be accessed and potentially manipulated by malicious actors. The issue affects versions prior to Firefox 54 and Firefox ESR 52.2, as well as Thunderbird versions before 52.2, indicating this was a widespread problem across multiple Mozilla products.
The root cause of this vulnerability lies in the browser's handling of DOM element references and memory cleanup processes during dynamic content updates. When a window object is removed from the DOM structure, the system should properly invalidate all references to that object and release associated memory. However, in this case, the "<track>" element maintains a stale reference to the replaced window, creating a use-after-free condition. This type of vulnerability falls under CWE-416, which specifically addresses the use of memory after it has been freed, and represents a classic memory safety issue that can lead to arbitrary code execution. The vulnerability operates through the HTML5 video element's track handling mechanism, where the browser's JavaScript engine fails to properly manage the lifecycle of window references within track element contexts.
The operational impact of CVE-2017-7750 is significant as it provides potential attackers with a pathway to achieve remote code execution on vulnerable systems. When exploited, this vulnerability can cause the browser to crash or potentially allow attackers to execute malicious code with the privileges of the user running the browser. The crash behavior is particularly concerning as it can be leveraged to deliver denial-of-service attacks or serve as a stepping stone for more sophisticated exploits. The vulnerability's exploitation typically requires the attacker to craft malicious web content that triggers the specific DOM manipulation sequence involving track elements and window replacements. This attack vector aligns with ATT&CK technique T1059.007 for script-based attacks and represents a common pattern in browser exploitation where memory corruption vulnerabilities are leveraged for privilege escalation.
Mitigation strategies for this vulnerability require immediate patching of affected software versions to ensure proper memory management and reference invalidation. Organizations should prioritize updating Firefox, Firefox ESR, and Thunderbird installations to versions that contain the necessary fixes for this use-after-free condition. The patch implementations typically involve strengthening the DOM element reference management logic and ensuring that all stale references are properly cleared when window objects are removed from the document structure. Additional defensive measures include implementing content security policies, restricting access to potentially malicious web content, and monitoring for unusual browser behavior that might indicate exploitation attempts. Security teams should also consider deploying browser hardening techniques and maintaining awareness of related vulnerabilities that might exploit similar memory management flaws, as this type of vulnerability often indicates broader issues within the application's memory handling architecture.