CVE-2026-117901 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 out-of-bounds write due to use-after-free conditions, this flaw arises when the browser retains access to a memory region that has already been deallocated by the system. In complex web environments involving dynamic DOM manipulation or intricate HTML parsing sequences, the application may attempt to read from or write to this invalid memory address. This scenario typically occurs when an object is destroyed while references to it are still active in other parts of the codebase, leading to undefined behavior that can be exploited by malicious actors.
From a technical perspective, use-after-free vulnerabilities allow attackers to manipulate program execution flow by controlling the contents of freed memory. If an attacker can influence what data occupies the reclaimed memory space before it is accessed again, they may achieve arbitrary code execution with the privileges of the user running the browser. This type of exploit often involves crafting specific HTML or JavaScript payloads that trigger the premature deallocation of a DOM element while maintaining references to it through event handlers or asynchronous operations. The subsequent access triggers the out-of-bounds write, potentially overwriting critical data structures such as function pointers or object vtables within the browser process memory space.
The operational impact of this vulnerability is severe, particularly for users who visit maliciously crafted websites or open compromised email attachments containing embedded web content. Successful exploitation could lead to remote code execution, allowing an attacker to install malware, steal sensitive credentials stored in the browser, or pivot further into a user's network infrastructure. Given that Firefox serves as a primary internet gateway for many enterprise and individual users, this vulnerability poses a significant risk to data confidentiality and system integrity. The attack vector is primarily classified under remote code execution via web-based interactions, requiring no physical access or local privilege escalation on the part of the attacker beyond convincing the user to load the malicious content.
Industry standards categorize this flaw under CWE-416, which denotes use after free errors in software development. In terms of offensive security frameworks, such vulnerabilities are frequently associated with MITRE ATT&CK techniques related to initial access and execution via browser-based exploits. The vulnerability highlights the importance of robust memory safety practices within web rendering engines, where complex interactions between JavaScript runtime environments and native C++ components create numerous opportunities for logic errors if reference counting or garbage collection mechanisms fail to synchronize correctly.
Mitigation strategies primarily involve applying the vendor-provided patches that address these specific memory management flaws in the DOM core and HTML parsing modules. Users should immediately update their Firefox installations to version 159, Firefox Extended Support Release (ESR) version 115.44, or ESR version 153.6, as these releases contain the necessary code corrections to prevent premature deallocation of objects while they are still in use. Additionally, organizations should enforce strict browser update policies and consider deploying content security policies that restrict inline scripts where possible to reduce the attack surface for such exploits. Security awareness training regarding suspicious web links and attachments remains a vital complementary control against social engineering tactics used to deliver these malicious payloads.