CVE-2026-100758 in Firefox
Summary
by MITRE • 09/29/2026
Sandbox escape in the DOM: Navigation component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
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Analysis
by VulDB Data Team • 09/29/2026
The identified vulnerability represents a critical failure in the browser's sandboxing mechanisms within the Document Object Model navigation component. This flaw allows content running with restricted privileges to escape its intended execution context and gain elevated access to system resources or sensitive data that should remain inaccessible under normal browsing conditions. Such sandbox escapes are among the most severe classes of web vulnerabilities because they effectively neutralize one of the primary defense layers against remote code execution attacks, which is the isolation between untrusted web content and the host operating system. The root cause typically involves improper validation of navigation targets or state management errors that allow an attacker to manipulate internal browser states in a way that bypasses security checks designed to prevent cross-origin data leakage or privilege escalation.
From a technical perspective, this issue likely stems from how the browser handles transitions between different document contexts and manages the lifecycle of window objects during complex navigation sequences. When a malicious webpage triggers specific DOM manipulations involving frame navigations or history API calls, it may exploit race conditions or logic errors in the security manager to trick the browser into treating untrusted content as trusted origin data. This misconfiguration enables the attacker to read cookies, local storage, or other sensitive attributes belonging to different origins that are normally protected by the Same-Origin Policy. The exploitation vector generally requires user interaction, such as clicking a crafted link or triggering an automated script within a compromised webpage, but once executed, it can lead to significant data exfiltration without further user consent.
The operational impact of this vulnerability is substantial for both individual users and enterprise environments relying on Firefox ESR versions. For end-users, successful exploitation could result in the theft of session tokens, authentication credentials, or personally identifiable information stored within browser storage mechanisms. In corporate settings where browsers are used to access internal web applications, a sandbox escape can serve as an initial foothold for attackers to pivot into internal networks by accessing sensitive intranet resources that should be isolated from public-facing websites. This undermines the trust model of modern web browsing and poses a significant risk to organizations implementing strict security policies around browser-based data handling.
To mitigate this threat, it is imperative to apply the provided patches immediately across all affected systems. The vulnerability has been resolved in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17. Organizations should prioritize updating their browser fleets to these versions or later releases where the security patches are integrated. Additionally, administrators can enforce automatic update policies through group policy objects or mobile device management solutions to ensure that all endpoints remain protected against known exploitation techniques associated with DOM-based sandbox escapes. Monitoring for unusual network traffic patterns originating from browsers may also help detect potential attempts to exploit this flaw before significant damage occurs.
This vulnerability aligns with Common Weakness Enumeration categories such as CWE-250, which covers execution with unnecessary privileges, and CWE-863, concerning incorrect authorization enforcement. In the context of the MITRE ATT&CK framework, it relates to techniques involving browser exploitation for initial access or privilege escalation, specifically those that leverage vulnerabilities in web browsers to bypass security restrictions. Understanding these classifications helps security teams better categorize similar incidents and refine their detection rules to identify attempts to exploit DOM-based navigation flaws in future threat landscapes.