CVE-2026-100819 in Firefox
Summary
by MITRE • 09/29/2026
Sandbox escape due to incorrect boundary conditions in the XPCOM 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 security flaw resides within the XPCOM component of Mozilla Firefox, representing a critical failure in boundary condition validation that facilitates sandbox escape vulnerabilities. In modern web browsers, the rendering engine operates under strict isolation principles to prevent malicious content from accessing sensitive system resources or user data. The XPCOM (Cross-Platform Component Object Model) architecture serves as a foundational framework for these components, managing interactions between different parts of the browser and external applications. When boundary conditions are not correctly enforced within this layer, it creates an opportunity for attackers to manipulate memory states in ways that bypass established security boundaries. This specific type of vulnerability is categorized under CWE-190, which addresses integer overflow or wraparound issues, often leading to out-of-bounds access when calculations involving array indices or buffer sizes exceed their expected limits due to improper validation logic.
The operational impact of this flaw is severe because it undermines the browser's primary defense mechanism against drive-by download attacks and cross-site scripting exploits that attempt to escalate privileges. By exploiting incorrect boundary conditions, a malicious actor can craft specially designed web content or scripts that trigger unintended behavior within the XPCOM subsystem. This allows code executed in a restricted sandbox environment to break out into higher-privilege contexts, potentially gaining access to local file systems, network interfaces, or other protected areas of the operating system. Such an escape effectively neutralizes the security model intended to isolate untrusted web content from the host machine, exposing users to risks including data theft, malware installation, and complete compromise of their computing environment. The vulnerability aligns with ATT&CK technique T1055, which covers process injection and other forms of code execution that leverage system APIs for unauthorized access, highlighting its potential use in advanced persistent threat scenarios where stealthy privilege escalation is required.
Mitigation strategies primarily rely on the timely application of vendor-provided patches to ensure that the underlying logic governing boundary checks has been corrected by Mozilla engineers. Users must update their installations to Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, or Firefox ESR 140.17 immediately upon availability. These versions contain specific code changes that enforce stricter validation of input parameters and array bounds within the XPCOM framework, thereby preventing the overflow conditions that lead to memory corruption and sandbox escapes. In addition to software updates, organizations should implement network-level controls such as web filtering proxies to block access to known malicious domains hosting exploit kits targeting this vulnerability. Furthermore, deploying endpoint detection and response solutions can help identify anomalous behavior patterns indicative of a successful exploitation attempt, providing an additional layer of defense in depth against sophisticated attacks that may bypass perimeter security measures.