CVE-2026-109715 in Firefox
Summary
by MITRE • 10/13/2026
Incorrect boundary conditions in the JavaScript Engine component. This vulnerability was fixed in Firefox 158, Firefox ESR 115.43, and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/13/2026
The identified security issue resides within the core JavaScript engine of Mozilla Firefox, specifically involving incorrect boundary conditions during memory access operations. This type of vulnerability typically arises when the runtime environment fails to properly validate array indices or buffer offsets before performing read or write actions on allocated memory regions. In complex scripting environments like SpiderMonkey, which powers Firefox's JavaScript execution, such errors can lead to out-of-bounds reads or writes if the engine does not strictly enforce limits against the actual size of data structures. The flaw suggests a lapse in static analysis or runtime checks that are designed to prevent access beyond the allocated boundaries of an object or array, allowing maliciously crafted scripts to interact with memory locations outside their intended scope.
From a technical perspective, incorrect boundary conditions often facilitate arbitrary read and write primitives when exploited successfully. An attacker could leverage this flaw by constructing specific JavaScript code that triggers the miscalculated index, thereby gaining unauthorized access to adjacent memory structures. This capability is particularly dangerous as it can be used to leak sensitive information stored in nearby memory locations or to overwrite critical data such as function pointers or object headers. Such manipulation undermines the integrity of the execution environment and serves as a foundational step for more complex attacks, including arbitrary code execution if combined with other techniques like heap spraying or type confusion vulnerabilities. The presence of this flaw indicates that under specific edge cases involving large arrays or complex nested objects, the engine's safety mechanisms were insufficient to contain the operation within safe limits.
The operational impact of this vulnerability is significant for users relying on Firefox and its derivatives for secure web browsing. If a malicious website exploits this boundary condition error, it could potentially lead to information disclosure, where sensitive data from other tabs or applications residing in memory might be exfiltrated. In more severe scenarios, successful exploitation allows an attacker to execute arbitrary code with the privileges of the user running the browser. This compromises the fundamental security model of web browsers, which rely on sandboxing and isolation to protect users from untrusted content. The ability to bypass these protections means that a single compromised webpage could serve as a vector for installing malware, stealing credentials, or conducting further attacks against the underlying operating system infrastructure.
To mitigate this risk, it is imperative to update all instances of Firefox to version 158 and ensure that Extended Support Release (ESR) users are running at least version 115.43 or ESR 153.5, as these releases contain the necessary patches for the JavaScript engine's boundary checks. Organizations should enforce automated patch management policies to ensure timely deployment of security updates across all endpoints. Additionally, implementing browser hardening techniques such as disabling unnecessary plugins and using content security policies can reduce the attack surface available to potential exploiters. Security teams should also monitor for indicators of compromise related to memory corruption events in JavaScript engines, as these may signal active exploitation attempts targeting this specific class of vulnerabilities before patches are fully deployed across all user bases.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-125, which describes Out-of-bounds Read, and potentially CWE-787, Out-of-bounds Write, depending on the exact nature of the memory access violation observed during exploitation attempts. In terms of attack tactics, this flaw supports techniques associated with MITRE ATT&CK technique T1059, specifically command execution via scripting interpreters, as it provides a pathway to achieve arbitrary code execution through JavaScript engine manipulation. Understanding these classifications helps in mapping the vulnerability to broader threat intelligence frameworks and prioritizing remediation efforts based on industry-standard risk assessments.