CVE-2026-100772 in Firefox
Summary
by MITRE • 09/29/2026
Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17.
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Analysis
by VulDB Data Team • 09/29/2026
The identified vulnerability represents a critical memory management error within the Document Object Model core and HTML components of Mozilla Firefox browsers. Specifically classified as an use-after-free condition, this flaw occurs when the application continues to reference a memory block after it has been deallocated or freed by the system. In the context of browser rendering engines, such errors typically arise during complex DOM manipulations where elements are dynamically added, removed, or modified via JavaScript interactions with HTML structures. When an object is destroyed but pointers or references to that object remain active within internal data structures, subsequent operations attempting to access these stale pointers result in undefined behavior. This can lead to the reading of corrupted memory contents or, more dangerously, the execution of arbitrary code if the freed memory region has been reallocated for malicious purposes by an attacker.
From a technical perspective, this vulnerability falls under CWE-416, which defines use-after-free as a class of software vulnerabilities resulting from improper handling of deallocated memory. The operational impact is severe because it allows remote attackers to potentially achieve arbitrary code execution on the victim's system through crafted web content. By hosting or manipulating a webpage that triggers specific DOM events and HTML parsing routines, an attacker can exploit the race condition between object destruction and subsequent access. This exploitation vector does not require user interaction beyond visiting the malicious site, making it a high-risk remote code execution vulnerability. The integrity of the browser's sandboxing mechanisms may be compromised if the memory corruption allows for control flow hijacking or data exfiltration from other tabs or processes sharing the same address space.
Industry frameworks such as MITRE ATT&CK categorize this type of exploitation under techniques related to initial access and privilege escalation, specifically leveraging software vulnerabilities in web browsers. The attack chain typically involves delivering a malicious payload via social engineering or drive-by download tactics that triggers the vulnerable DOM operations. Once executed, the attacker gains a foothold within the browser process context, which can serve as a stepping stone for further lateral movement if additional security controls are not in place. The severity is amplified by the widespread adoption of Firefox across enterprise and consumer environments, meaning successful exploitation could lead to significant data breaches or system compromise on a large scale.
Mitigation strategies primarily rely on applying the vendor-provided patches that address these memory management flaws. Users must update their browsers to Firefox ESR 153.4, Firefox 157, or Firefox ESR 140.17 immediately upon availability. These updates contain code changes that ensure proper lifecycle management of DOM objects and HTML elements, preventing references from persisting after deallocation. In addition to patching, organizations should enforce strict content security policies to restrict the execution of untrusted scripts and limit access to sensitive APIs. Network-level monitoring can also help detect anomalous traffic patterns associated with exploitation attempts, although technical mitigation through software updates remains the most effective defense against this specific class of vulnerability.