CVE-2017-7802 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur when manipulating the DOM during the resize event of an image element. If these elements have been freed due to a lack of strong references, a potentially exploitable crash may occur when the freed elements are accessed. This vulnerability affects Thunderbird < 52.3, Firefox ESR < 52.3, and Firefox < 55.
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Analysis
by VulDB Data Team • 11/26/2025
This vulnerability represents a critical use-after-free condition that manifests during dynamic DOM manipulation operations involving image elements during resize events. The flaw occurs when the browser's rendering engine fails to maintain proper reference counting or garbage collection mechanisms during the lifecycle of DOM elements, specifically when image elements undergo size changes. The vulnerability is particularly dangerous because it leverages the timing-sensitive nature of event handling and memory management within web browsers. When an image element is resized, the browser must update its associated DOM nodes and potentially reallocate memory resources, creating a window where freed memory references can be accessed by subsequent operations.
The technical implementation of this vulnerability exploits the fundamental memory management principles that govern how browsers handle dynamic content. During resize operations, the browser's JavaScript engine interacts with the DOM tree and underlying C++ objects that represent image elements, creating complex reference relationships that can break down under certain conditions. When elements lack strong references, they become eligible for garbage collection, but if resize event handlers attempt to access these freed objects, the memory access violation manifests as a crash. This behavior aligns with CWE-416, which describes the use of freed memory vulnerability, and demonstrates how improper memory management during event processing can create exploitable conditions.
The operational impact of this vulnerability extends beyond simple browser crashes, as it provides potential attackers with a mechanism to execute arbitrary code within the browser context. Attackers can craft malicious web pages that manipulate image elements in ways that trigger the specific memory access patterns leading to exploitation. The vulnerability affects major browser versions including Thunderbird 52.2 and earlier, Firefox ESR 52.2 and earlier, and Firefox 54 and earlier, representing a significant attack surface across widely used email and web clients. The timing and conditions required for exploitation make this a sophisticated target for advanced persistent threats, as demonstrated by various exploit frameworks that have leveraged similar use-after-free conditions in the past. The vulnerability's presence in both desktop and mobile browser implementations underscores the importance of comprehensive memory management across all client platforms.
Mitigation strategies for this vulnerability require immediate patching of affected browser versions to address the underlying memory management issues in the DOM handling code. Organizations should implement browser hardening measures including disabling unnecessary JavaScript features, implementing content security policies, and using sandboxing technologies to limit potential exploitation impact. The fix typically involves strengthening reference counting mechanisms during DOM element lifecycle management and ensuring proper memory validation before accessing objects during event processing. Security teams should monitor for exploitation attempts through network traffic analysis and endpoint detection systems, as the vulnerability may be exploited through drive-by downloads or malicious websites. Additionally, user education regarding safe browsing practices and avoiding untrusted content remains crucial for reducing attack surface, though the vulnerability's nature makes it particularly challenging to defend against through user awareness alone. The remediation process should also include comprehensive testing of browser updates to ensure that similar memory management issues have been addressed across all affected components.