CVE-2026-117951 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the DOM: Core & HTML 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 • 10/27/2026
The identified vulnerability represents a critical memory management error within the Document Object Model core and HTML components of Mozilla Firefox browsers. Specifically classified as an use-after-free condition, this flaw occurs when the software continues to reference a block of memory that has already been deallocated or freed by the system. In the context of web browser engines, such errors typically arise during complex interactions between JavaScript execution and DOM manipulation routines where object lifecycles are not strictly synchronized with garbage collection mechanisms. When an attacker can trigger this specific sequence, they gain the ability to access invalid memory addresses that may contain sensitive data or control flow pointers previously held by other objects in the heap space.
From a technical perspective, use-after-free vulnerabilities exploit the disconnect between when resources are released and when references to those resources are dereferenced. In Firefox's rendering engine, this likely involves scenarios where DOM nodes are removed from the document tree while active event listeners or JavaScript variables still hold pointers to them. If an attacker can craft a malicious webpage that forces these conditions through rapid DOM updates or specific CSS interactions, they can manipulate the heap layout. By carefully controlling what data is allocated into the freed memory space, an attacker can achieve arbitrary code execution with the privileges of the browser process. This transforms a simple memory corruption bug into a potent remote code execution vector capable of compromising the entire host system if sandboxing mechanisms are bypassed or fail to contain the exploit.
The operational impact of this vulnerability is severe due to its potential for remote exploitation via standard web browsing activities. Users visiting compromised websites, clicking on malicious links in emails, or loading untrusted content from third-party services could inadvertently trigger the flaw without any additional interaction required beyond normal page rendering. The consequences range from complete system compromise and data theft to denial of service conditions if the memory corruption leads to a browser crash. Given that Firefox is widely used across enterprise environments and personal devices, this vulnerability poses a significant risk to organizational security postures, potentially serving as an initial access vector for broader cyberattacks including ransomware deployment or espionage operations targeting sensitive corporate information stored locally on affected machines.
Mitigation strategies primarily rely on the immediate application of vendor-provided patches. The issue has been resolved in Firefox version 159 and extended support release versions 115.44 and 153.6, which implement stricter memory management checks and improved lifecycle tracking for DOM objects to prevent dangling pointer dereferences. Organizations should prioritize updating all endpoints running affected browser versions to ensure the patch is applied. In environments where immediate patching is not feasible due to compatibility concerns, network-level controls such as web filtering proxies can be configured to block access to known malicious domains or restrict JavaScript execution on untrusted sites. Additionally enabling sandboxing features and keeping operating system security patches current provides defense-in-depth measures that limit the impact of any successful exploitation attempt by isolating browser processes from critical system resources.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-416, which defines use-after-free errors as a distinct category of memory safety issues. From an offensive security perspective, it maps to MITRE ATT&CK techniques related to initial access and execution via web browsers, specifically leveraging client-side software vulnerabilities for privilege escalation or code injection. Understanding these mappings helps security teams prioritize remediation efforts based on industry-standard risk frameworks and ensures that detection rules can be tuned to identify exploitation patterns associated with heap spraying and memory corruption attacks commonly seen in browser-based exploits.