CVE-2018-5096 in Firefox ESR
Summary
by MITRE
A use-after-free vulnerability can occur while editing events in form elements on a page, resulting in a potentially exploitable crash. This vulnerability affects Firefox ESR < 52.6 and Thunderbird < 52.6.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2018-5096 represents a critical use-after-free flaw that manifests during the manipulation of form elements within web pages. This issue specifically impacts Mozilla Firefox Extended Support Release versions prior to 52.6 and Thunderbird versions below 52.6, creating a significant security risk for users operating these affected software versions. The flaw occurs when the browser processes event editing operations on form elements, leading to memory management inconsistencies that can be exploited by malicious actors. The technical nature of this vulnerability places it squarely within the realm of memory corruption vulnerabilities, which are particularly dangerous due to their potential for arbitrary code execution.
The underlying technical mechanism involves a classic use-after-free condition where the browser's memory management system attempts to access memory that has already been freed during event handling operations on form elements. When users interact with form fields or manipulate events associated with these elements, the browser's rendering engine may release memory resources while still maintaining references to them. This creates a scenario where malicious code could potentially overwrite the freed memory with attacker-controlled data, leading to a crash that could be leveraged for more severe exploitation. The vulnerability operates at the intersection of web rendering and memory management, making it particularly challenging to mitigate as it requires careful handling of event lifecycle management within the browser's JavaScript engine.
The operational impact of this vulnerability extends beyond simple browser instability, as it provides a potential pathway for remote code execution attacks. Attackers could craft malicious web pages that, when loaded in affected browsers, would trigger the use-after-free condition and potentially execute arbitrary code with the privileges of the browser process. This risk is particularly concerning given that form elements are commonly encountered in web browsing activities, making the exploitation vector highly accessible. The vulnerability affects not just regular browsing scenarios but also email client functionality in Thunderbird, expanding the potential attack surface. According to CWE classification, this vulnerability maps to CWE-416, which specifically addresses the use of freed memory conditions, while the ATT&CK framework would categorize this under privilege escalation and code execution techniques.
Mitigation strategies for CVE-2018-5096 primarily focus on immediate software updates to versions that contain patches addressing the memory management flaw. Organizations should prioritize updating Firefox ESR to version 52.6 or later and Thunderbird to version 52.6 or higher, as these releases include fixes that properly handle event lifecycle management during form element operations. Additionally, administrators should consider implementing browser hardening measures such as disabling unnecessary JavaScript features, implementing content security policies, and using sandboxing techniques to limit the potential impact of successful exploitation attempts. Network-level protections such as web application firewalls and intrusion detection systems can also help detect and block malicious web content designed to exploit this vulnerability. Security teams should also conduct regular vulnerability assessments to ensure that all systems running affected software versions are properly patched and monitored for potential exploitation attempts.