CVE-2026-117974 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the XML 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 classified as an out-of-bounds write due to use-after-free conditions within the XML parsing component of Mozilla Firefox browsers. This specific flaw arises when the application attempts to access or manipulate memory regions that have already been deallocated by the system's garbage collector or explicit free operations. In complex web applications, particularly those involving dynamic content rendering and extensive DOM manipulation, the lifecycle management of objects can become intricate. If a reference to an object is retained after its underlying memory has been freed, subsequent operations on that dangling pointer lead to undefined behavior. The XML component handles the parsing and processing of Extensible Markup Language data, which often involves creating numerous temporary objects during tokenization and tree construction phases. A failure in properly nullifying references or synchronizing access across threads can result in these stale pointers being dereferenced, allowing an attacker to write arbitrary data into memory locations that may no longer belong to the intended object structure.
From a technical perspective, this vulnerability falls under CWE-416, which defines use-after-free errors as a subset of improper resource release vulnerabilities. The exploitation potential is significant because modern browsers employ various security mitigations such as Address Space Layout Randomization and heap spraying protections. However, sophisticated attackers can leverage the predictable nature of certain memory allocation patterns to control the contents of the freed memory region. By carefully crafting malicious XML payloads that trigger specific parsing paths within Firefox's engine, an attacker can force the browser to allocate new objects in the same memory slots previously occupied by the freed XML-related structures. When the vulnerable code subsequently writes data through the dangling pointer, it effectively overwrites these newly allocated objects. This mechanism allows for precise control over heap contents, which is a foundational step toward achieving arbitrary code execution or bypassing sandbox restrictions that isolate web content from the host operating system.
The operational impact of this vulnerability extends beyond simple application crashes to severe security compromises including remote code execution and privilege escalation. If successfully exploited, an attacker could execute malicious scripts with the same privileges as the user running the browser, potentially leading to data theft, installation of malware, or complete compromise of the underlying system. The risk is exacerbated by the fact that XML parsing often occurs in response to external inputs such as RSS feeds, web services APIs, and embedded content from third-party sites. This means that merely visiting a compromised website or loading a malicious document could trigger the vulnerability without any user interaction beyond normal browsing activities. Furthermore, because this issue affects multiple versions including long-term support releases like Firefox ESR 153.6, organizations relying on stable browser environments for enterprise operations face prolonged exposure if patching cycles are delayed.
Mitigation strategies must prioritize immediate software updates to ensure that the patched code paths in Firefox version 159 and the specified ESR branches are deployed across all client systems. Security teams should verify that automatic update mechanisms are enabled and functioning correctly to prevent users from remaining on vulnerable versions for extended periods. In environments where immediate patching is not feasible, network-level controls such as web application firewalls can be configured to inspect incoming XML traffic for patterns indicative of exploitation attempts, although this approach has limitations due to the complexity of valid XML structures. Additionally, enabling strict Content Security Policy headers and disabling unnecessary browser features that process external data sources can reduce the attack surface. Continuous monitoring for anomalous memory usage or crashes in the Firefox process can also serve as an early warning indicator for potential exploitation activities in real-time environments.