CVE-2026-109707 in Firefox
Summary
by MITRE • 10/13/2026
Sandbox escape due to use-after-free in the Networking component. This vulnerability was fixed in Firefox 158 and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/13/2026
The identified security flaw represents a critical memory corruption issue within the Mozilla Firefox networking subsystem, specifically categorized as an out-of-bounds write resulting from a use-after-free condition. In software engineering terms, this vulnerability arises when a program continues to reference a pointer after the memory it points to has been deallocated or freed by another part of the system. This scenario creates a race condition where the application may attempt to write data into a memory region that is no longer reserved for its intended purpose, potentially overwriting adjacent objects in the heap structure. Such errors are particularly dangerous because they allow an attacker to manipulate the internal state of the browser process with arbitrary precision, effectively bypassing standard memory safety protections like Address Space Layout Randomization and Data Execution Prevention if exploited correctly.
From a technical perspective, this vulnerability falls under CWE-416, which defines use-after-free as a class of software vulnerabilities where a pointer is used after it has been freed. The specific manifestation in the networking component suggests that network-related objects or buffers were not properly managed during asynchronous operations or connection teardowns. When an attacker can trigger the deallocation of these resources while they are still being accessed, they gain control over what data gets written to which memory addresses. This capability is significant because it allows for arbitrary code execution within the context of the browser process, provided that the overwritten memory contains function pointers or object headers that dictate subsequent program flow.
The operational impact of this vulnerability is severe, as successful exploitation could lead to remote code execution on the victim's machine without any user interaction beyond visiting a maliciously crafted webpage. Attackers can leverage this flaw to install malware, steal sensitive credentials stored in the browser, or establish persistent access to the system. The risk is amplified by the fact that modern browsers handle complex network requests involving multiple protocols and asynchronous callbacks, increasing the attack surface for triggering these race conditions. Consequently, any user running an affected version of Firefox remains at high risk when interacting with untrusted web content designed specifically to exploit this memory corruption flaw.
This incident aligns closely with MITRE ATT&CK technique T1203, which covers exploitation for client execution, and more broadly with the initial access phase where attackers deliver malicious payloads via compromised or weaponized websites. The vulnerability highlights the importance of rigorous memory management practices in high-level applications that interface directly with system resources. Developers must ensure strict ownership semantics for network objects to prevent dangling pointers from persisting beyond their valid lifecycle.
Mitigation strategies primarily involve applying the vendor-provided patches immediately upon release, as indicated by the fixes included in Firefox version 158 and Firefox Extended Support Release (ESR) version 153.5. Organizations should enforce automated update policies for all endpoints running affected browser versions to minimize exposure windows. Additionally, security teams can employ application control solutions or sandboxing technologies that restrict network access privileges for browsers where possible, thereby limiting the potential blast radius of a successful exploitation attempt even if the underlying vulnerability remains unpatched in legacy systems awaiting upgrade cycles.