CVE-2026-117941 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the DOM: CSS Object Model 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's CSS Object Model implementation, specifically classified as an use-after-free condition. This type of flaw occurs when software continues to reference a block of memory after it has been deallocated or freed by the system. In the context of browser rendering engines, this typically involves internal data structures that track style rules, computed styles, or layout information associated with DOM elements. When these objects are destroyed due to changes in the document structure or explicit removal from the tree, references held elsewhere may not be properly nullified or updated. Consequently, subsequent operations attempting to access these stale pointers interact with memory regions that have already been returned to the allocator pool and potentially reused for other purposes.
From a technical perspective, this flaw allows an attacker who can craft malicious web content to trigger specific sequences of DOM manipulation and CSS style application that lead to the premature release of critical objects while active references remain in use. The browser's rendering pipeline may attempt to read or write data through these dangling pointers during layout calculations or style resolution phases. Because modern browsers employ various memory safety mechanisms, such as heap randomization and guard pages, exploitation is not guaranteed but remains feasible under specific conditions. Successful exploitation could lead to arbitrary code execution with the privileges of the browser process, allowing an attacker to bypass security boundaries established by the same-origin policy and potentially compromise the underlying operating system if further exploits are chained together.
The operational impact of this vulnerability extends beyond simple application crashes or denial of service scenarios. While a crash is a common immediate symptom resulting from accessing invalid memory addresses, the primary concern lies in the potential for remote code execution. An attacker could leverage this flaw to inject and execute arbitrary commands on the victim's machine by carefully controlling the contents of the freed memory region before it is reallocated. This capability undermines the fundamental security model of web browsers, which rely heavily on process isolation and sandboxing to protect user data and system integrity. Users visiting compromised or maliciously crafted websites could find their systems fully compromised without any additional interaction beyond loading the page.
Industry standards categorize this vulnerability under CWE-416, Use After Free, which highlights the failure to properly manage memory lifecycle in software development. In terms of attack vectors, this aligns with MITRE ATT&CK techniques related to client-side exploitation and potentially privilege escalation depending on the browser's sandbox configuration. The fix implemented in Firefox version 159, as well as the extended support releases versions 115.44 and 153.6, addresses these issues by ensuring that references are properly invalidated upon object destruction or by implementing more robust memory tracking mechanisms within the CSSOM subsystem.
To mitigate risks associated with this class of vulnerabilities, organizations should prioritize immediate patching to ensure all client systems run the patched versions mentioned above. For users unable to update immediately due to compatibility constraints, deploying network-level security controls such as web filtering proxies can help block access to known malicious domains or suspicious content patterns that might attempt to exploit this flaw. Additionally, enabling advanced browser sandboxing features and keeping operating system memory protection mechanisms like ASLR enabled provides additional layers of defense against exploitation attempts. Regular vulnerability scanning and monitoring for emerging exploits targeting browser components are essential practices in maintaining a secure browsing environment.