CVE-2026-117864 in Firefox
Summary
by MITRE • 10/27/2026
Sandbox escape in the Form Manager component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/28/2026
The identified security issue represents a critical sandbox escape vulnerability located within the Form Manager component of Mozilla Firefox browsers, specifically affecting versions prior to 159 and Firefox Extended Support Release (ESR) version 153.6. This type of flaw is particularly severe because it allows an attacker to bypass the browser's multi-process architecture security model, which is designed to isolate web content from sensitive system resources. By exploiting this vulnerability, a malicious actor can execute arbitrary code with elevated privileges outside the restricted sandbox environment that normally confines untrusted web pages. The Form Manager component handles the storage and retrieval of form data such as usernames, passwords, addresses, and other user inputs. When an attacker crafts a specially designed webpage or script that interacts improperly with this component, they can trigger memory corruption or logic errors that break out of the sandbox boundaries. This escape effectively neutralizes one of the primary defense mechanisms against drive-by download attacks and cross-site scripting exploits, as it grants the malicious code direct access to the underlying operating system environment rather than keeping it confined within a limited execution context.
From a technical perspective, vulnerabilities in form management often stem from improper handling of data structures or insufficient validation of inputs passed between different browser processes. In this case, the flaw likely involves a failure to properly sanitize or validate specific attributes or methods invoked during the processing of stored form data. This could involve buffer overflows, use-after-free conditions, or type confusion errors that allow an attacker to manipulate memory pointers or control flow execution paths. When these internal checks are bypassed, the malicious payload gains the ability to interact with system APIs and file systems directly. The operational impact is profound because it transforms a typical web-based attack into a full device compromise. An adversary could use this escape vector to install persistent malware, exfiltrate sensitive personal information stored locally by the browser such as saved credentials or autofill data, or pivot further into internal network resources if the user has access to them. This significantly increases the risk profile for both individual users and enterprise environments relying on Firefox for secure web browsing.
The classification of this vulnerability aligns with Common Weakness Enumeration (CWE) standards, specifically referencing CWE-269 which pertains to Improper Privilege Management, or potentially CWE-125 Out-of-bounds Read if the escape is facilitated by memory corruption techniques that allow reading arbitrary memory locations leading to control flow hijacking. In terms of offensive security frameworks like MITRE ATT&CK, this exploit maps directly to Tactic 6: Defense Evasion and Technique T1055 Process Injection or potentially T1218 Signed Binary Proxy Execution if the escape involves leveraging legitimate system binaries. The ability to break out of a sandbox is considered one of the highest severity outcomes in browser security research because it undermines the fundamental trust model that allows users to browse the internet with relative safety against untrusted content providers.
Mitigation for this vulnerability requires immediate action by updating all affected instances of Firefox and Firefox ESR to version 159 or later, which includes the necessary patches to correct the logic errors within the Form Manager component. Organizations should enforce automated patch management policies to ensure that browser updates are applied promptly across all endpoints. Additionally, security teams can implement application control solutions such as Windows Defender Application Control (WDAC) or AppLocker to restrict the execution of unauthorized binaries and scripts, thereby adding a layer of defense even if a sandbox escape occurs. Users should also be educated on the risks of visiting untrusted websites and disabling unnecessary browser features that might expand the attack surface, although relying solely on user behavior is insufficient given the severity of this specific flaw. Regular vulnerability scanning and monitoring for indicators of compromise related to known exploit kits targeting Firefox can further aid in detecting potential attempts to leverage this sandbox escape before a full system compromise takes place.