CVE-2019-9790 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur when a raw pointer to a DOM element on a page is obtained using JavaScript and the element is then removed while still in use. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 60.6, Firefox ESR < 60.6, and Firefox < 66.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2019-9790 represents a critical use-after-free condition that manifests in web browsers when JavaScript code interacts with DOM elements through raw pointers. This flaw occurs when developers or scripts obtain direct references to DOM elements and subsequently manipulate them while those elements are being removed from the document structure. The underlying technical issue stems from improper memory management where freed memory locations are accessed after the original object has been deallocated, creating a potential attack surface for malicious actors. The vulnerability specifically impacts Mozilla Firefox and Thunderbird applications, with affected versions including Firefox ESR before 60.6, Firefox before 66, and Thunderbird before 60.6, indicating a widespread exposure across multiple browser implementations.
The operational impact of this vulnerability extends beyond simple application crashes to potentially enable remote code execution in carefully crafted attack scenarios. When a DOM element is removed from the document while still referenced by JavaScript code, the browser's memory management system may prematurely free the associated memory structures. If subsequent JavaScript operations attempt to access this freed memory through the raw pointer, the application experiences undefined behavior that can manifest as crashes, memory corruption, or more severe exploitation opportunities. The use-after-free condition falls under CWE-416, which specifically addresses the use of memory after it has been freed, making this vulnerability particularly dangerous in the context of browser security where attackers can leverage such conditions to execute arbitrary code with the privileges of the compromised browser process.
Security researchers have classified this vulnerability as particularly concerning due to its potential for exploitation in the browser context where attackers can leverage the JavaScript environment to trigger the memory corruption. The attack vector typically involves constructing malicious web pages that manipulate DOM elements in ways that create the use-after-free condition, potentially leading to privilege escalation or complete system compromise. Organizations using affected browser versions should consider this vulnerability in their risk assessments, particularly given that the flaw affects both regular Firefox releases and the extended support release versions that many enterprises continue to use for stability. The vulnerability demonstrates the complexity of modern web browser security where high-level scripting languages like JavaScript interact with low-level memory management systems, creating intricate attack surfaces that require careful handling of object lifecycles and memory references.
Mitigation strategies for CVE-2019-9790 primarily focus on immediate version updates to patched browser releases, which address the underlying memory management issues in the JavaScript engine and DOM handling components. Organizations should prioritize deployment of Firefox 60.6 ESR, Firefox 66, or Thunderbird 60.6 updates to eliminate the vulnerability exposure. Additional protective measures include implementing content security policies to limit script execution capabilities, enabling sandboxing features where available, and conducting regular security assessments of web applications that may interact with potentially vulnerable browser versions. The ATT&CK framework categorizes this vulnerability under techniques involving memory corruption and privilege escalation, emphasizing the need for comprehensive security controls that address both the immediate patching requirements and broader defensive measures against similar memory safety issues. Network security teams should also monitor for indicators of compromise related to exploitation attempts targeting this vulnerability, particularly in environments where legacy browser versions may still be in use.