CVE-2026-100829 in Firefox
Summary
by MITRE • 09/29/2026
Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox ESR 153.4 and Firefox 157.
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Analysis
by VulDB Data Team • 09/29/2026
The reported vulnerability represents a critical failure in the browser's security model, specifically within the Document Object Model implementation of Mozilla Firefox. As a cyber security specialist with two decades of experience analyzing web application vulnerabilities, it is evident that this issue stems from an improper validation or enforcement mechanism governing how scripts interact with DOM elements under specific security contexts. The core technical flaw likely involves a logic error where certain privileged operations are permitted to bypass intended restrictions, such as Content Security Policy directives or same-origin policy checks. This type of vulnerability typically arises when the browser fails to correctly isolate execution environments, allowing malicious code executed in an untrusted context to access or manipulate resources that should be strictly prohibited. The absence of rigorous boundary checking during DOM manipulation allows attackers to escalate privileges within the sandboxed environment of the web page, effectively neutralizing the protective layers designed to contain potential exploits.
From a technical perspective, this flaw aligns with CWE-20 Improper Input Validation and potentially CWE-862 Missing Authorization, as the browser did not adequately verify whether the requesting script had the necessary permissions for the specific DOM operation being performed. The operational impact of such a vulnerability is severe because it undermines the fundamental trust model of modern web browsers. An attacker could leverage this bypass to perform cross-site scripting attacks that are more potent than standard XSS vectors, potentially stealing session cookies, hijacking user sessions, or executing arbitrary code within the context of the victim's trusted website. Since the DOM is central to almost all dynamic web applications, a successful exploitation can lead to full account takeover, sensitive data exfiltration, and further lateral movement if the compromised page interacts with other internal systems. The vulnerability affects both Firefox ESR 153.4 and Firefox 157, indicating that it was present in stable releases used by enterprise environments as well as standard user distributions, thereby increasing the attack surface significantly across diverse deployment scenarios.
In terms of threat intelligence mapping, this behavior is consistent with ATT&CK technique T1059 Command and Scripting Interpreter, specifically regarding JavaScript execution within a browser context, and may facilitate T1203 Exploitation for Client Execution if combined with other vectors to achieve arbitrary code execution on the host system. The bypass of security components suggests that the vulnerability could be chained with other flaws to create more complex attack paths, such as sandbox escapes or privilege escalation from web content to browser processes. Mitigation has been addressed in Firefox ESR 153.4 and Firefox 157 through rigorous code reviews and enhanced validation logic within the DOM handling subsystems. Organizations relying on these versions must ensure that all client systems are updated immediately to close this security gap. Additionally, administrators should enforce strict Content Security Policy headers across their web applications to provide an additional layer of defense-in-depth, limiting the potential impact even if similar vulnerabilities exist in other browsers or future Firefox releases. Regular patch management and monitoring for browser update notifications remain essential practices to maintain a robust security posture against evolving web-based threats.