CVE-2017-5442 in Firefox
Summary
by MITRE
A use-after-free vulnerability during changes in style when manipulating DOM elements. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 52.1, Firefox ESR < 45.9, Firefox ESR < 52.1, and Firefox < 53.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2017-5442 represents a critical use-after-free flaw that occurs during dynamic style manipulation of document object model elements within web browsers. This type of vulnerability falls under the common weakness enumeration CWE-416 which specifically addresses use after free conditions where memory is accessed after it has been freed, creating potential exploitation opportunities for malicious actors. The flaw manifests when browsers process changes to CSS styles applied to DOM elements, particularly during rapid or complex style modifications that trigger memory management operations.
The technical implementation of this vulnerability exploits the browser's rendering engine's handling of memory allocation and deallocation during style updates. When DOM elements undergo style modifications, the browser's JavaScript engine interacts with the underlying C++ code that manages memory for these elements. The use-after-free condition occurs when the browser attempts to access memory that has already been freed during the style change process, potentially leading to memory corruption that can be leveraged for remote code execution. This issue affects multiple browser versions including Thunderbird versions prior to 52.1, Firefox Extended Support Release versions before 45.9 and 52.1, and Firefox versions before 53, indicating a widespread impact across the browser ecosystem.
The operational impact of this vulnerability is significant as it can be exploited remotely through malicious web content without requiring user interaction. Attackers can craft web pages that trigger the specific sequence of DOM manipulations and style changes that lead to the use-after-free condition, potentially resulting in arbitrary code execution on vulnerable systems. This makes the vulnerability particularly dangerous in phishing campaigns or when users visit compromised websites. The crash behavior associated with this flaw provides attackers with a reliable method to achieve remote code execution by carefully controlling memory corruption patterns that can be leveraged to bypass modern exploit mitigations such as address space layout randomization and data execution prevention mechanisms.
Organizations and users should prioritize immediate patching of affected browser versions to mitigate this vulnerability. The affected software versions represent a substantial attack surface that requires urgent remediation. Security teams should implement network monitoring to detect potential exploitation attempts and consider deploying web application firewalls or content filtering solutions as additional defensive measures. The vulnerability demonstrates the importance of thorough memory management testing in browser rendering engines and highlights the need for continuous security assessment of complex web technologies. Organizations should also consider implementing browser hardening measures and user education regarding the risks of visiting untrusted websites, as the exploitation of this vulnerability can occur without any user interaction or specific actions beyond normal browsing behavior.