CVE-2026-117870 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 159, Firefox ESR 115.44, and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/28/2026
The identified vulnerability represents a critical memory management error within the Mozilla SpiderMonkey JavaScript engine, specifically classified as an out-of-bounds write resulting from a use-after-free condition. This type of flaw occurs when the application continues to use a pointer after the memory it points to has been reallocated or freed, leading to undefined behavior that can be exploited by malicious actors. In the context of web browsers like Firefox, this vulnerability resides in the core component responsible for parsing and executing JavaScript code, which is frequently invoked during normal browsing activities involving dynamic content, complex scripts, or third-party plugins. The presence of such a flaw indicates a failure in reference counting mechanisms or garbage collection logic within the engine's internal data structures, allowing an attacker to manipulate memory state after it has been released back to the system for reuse by other processes or objects.
From a technical perspective, use-after-free vulnerabilities are particularly dangerous because they allow attackers to achieve arbitrary code execution with high reliability when combined with specific exploitation techniques such as heap spraying or type confusion attacks. By carefully crafting malicious JavaScript payloads, an adversary can trigger the premature deallocation of critical memory structures and then force their reallocation with controlled data. This manipulation enables the attacker to overwrite function pointers, object headers, or other sensitive memory locations, effectively hijacking the control flow of the browser process. The severity is further amplified by the fact that modern browsers operate in sandboxed environments; however, a successful exploitation of this vulnerability could potentially allow an attacker to escape these sandboxes and gain access to the underlying operating system, compromising user privacy, integrity, and confidentiality.
The operational impact of this vulnerability extends beyond individual users who visit compromised websites or receive malicious emails with embedded scripts. It poses a significant risk to organizations relying on Firefox for secure web browsing, as it can serve as an initial vector for broader network intrusions. Attackers often leverage such vulnerabilities in drive-by download attacks where no user interaction is required beyond visiting a specially crafted webpage. The ability to execute arbitrary code means that sensitive data stored locally or accessed through authenticated sessions could be exfiltrated without detection. Furthermore, the persistence of this flaw across multiple versions indicates it may have been present for some time before being identified and patched, increasing the window of exposure for unpatched systems.
Mitigation strategies primarily involve ensuring that all instances of Firefox are updated to version 159 or later, including the Extended Support Release (ESR) branches at versions 115.44 and 153.6 respectively. These updates contain the necessary code changes to correct the memory management logic within the JavaScript engine, preventing the premature freeing of objects that are still in use. In environments where immediate patching is not feasible due to compatibility concerns or operational constraints, network-level defenses such as web application firewalls and intrusion detection systems can be configured to detect and block known exploit patterns associated with this vulnerability. Additionally, enabling strict content security policies and disabling unnecessary JavaScript execution on untrusted sites can reduce the attack surface available to potential adversaries exploiting this flaw.
This incident aligns with common weakness enumeration standards that highlight memory safety issues as a primary source of software vulnerabilities. Specifically, it corresponds to CWE-416 which describes use-after-free conditions leading to unexpected behavior and security breaches. In terms of tactical classification within the MITRE ATT&CK framework, this vulnerability facilitates initial access through technique T1189 Drive-by Compromise, where attackers exploit weaknesses in web browsers or plugins to install malware on victim systems without direct user interaction. The remediation effort underscores the importance of continuous monitoring and rapid deployment of security patches for core browser components that handle untrusted input from the internet. Organizations should prioritize updating their endpoints to mitigate the risk associated with this high-severity memory corruption flaw and ensure that automated update mechanisms are functioning correctly to prevent future exposure to similar vulnerabilities in other software components.