CVE-2026-117882 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the Layout 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 resulting from a use-after-free condition within the Layout component of Mozilla Firefox browsers. This specific class of flaw occurs when the application continues to reference a block of memory that has already been freed by the system's garbage collector or explicit deallocation routines. In the context of browser rendering engines, such as Gecko which powers Firefox, layout calculations are computationally intensive and involve frequent allocation and deallocation of objects representing DOM nodes, style rules, and visual frames. When an object is destroyed but a dangling pointer remains active within the execution flow, subsequent operations may inadvertently write data to this invalid memory address rather than allocating new safe storage. This behavior violates fundamental principles of secure coding by allowing writes into memory regions that are no longer owned by the application process for those specific objects.
From a technical perspective, use-after-free vulnerabilities in browser rendering engines often arise due to complex asynchronous operations or race conditions where references to layout frames are not properly invalidated after their parent containers are removed from the document tree. The vulnerability exploited this logic flaw within the Layout component, allowing an attacker who could craft malicious web content to trigger the premature deallocation of a critical layout object while retaining access to it through other active references. By carefully controlling the timing and sequence of DOM manipulations or CSS property changes, an adversary can force the browser into a state where freed memory is reused for unrelated purposes or overwritten with controlled data patterns. This mechanism bypasses standard sandboxing protections because the exploit operates within the same process space as the renderer, leveraging the inherent trust placed in layout calculations to execute arbitrary code logic through heap corruption techniques such as spray-and-pray methods or type confusion attacks that manipulate object headers and vtables.
The operational impact of this vulnerability is severe, potentially leading to remote code execution with the privileges of the user running the browser application. If successfully exploited, an attacker could gain full control over the victim's system by executing arbitrary commands, installing malware, stealing sensitive credentials stored in memory or on disk, or establishing persistent backdoors for further lateral movement within a network environment. The risk is amplified because web-based attacks can be delivered via phishing campaigns, compromised websites, or drive-by downloads without requiring any user interaction beyond visiting the malicious page. Given that Firefox maintains significant market share across enterprise and consumer environments, this vulnerability poses a substantial threat to data integrity and confidentiality for millions of users who rely on secure browsing practices.
Mitigation strategies primarily involve applying the vendor-provided patches released in Firefox version 159, as well as the extended support releases at versions ESR 115.44 and ESR 153.6. These updates contain code changes that enforce stricter reference counting mechanisms or implement safe pointer invalidation protocols to ensure that memory is not accessed after it has been released. Organizations should prioritize updating all endpoints running affected browser versions immediately to close this attack vector. Additionally, security teams can employ application whitelisting policies and restrict script execution on untrusted domains through Content Security Policy configurations to reduce the likelihood of successful exploitation even if similar vulnerabilities exist in future releases. Monitoring for anomalous memory usage patterns or unexpected process behavior may also aid in detecting attempted exploits in real-time environments where patching delays are unavoidable.
This incident aligns with Common Weakness Enumeration identifier CWE-416, which describes use-after-free conditions as a significant category of software defects leading to undefined behavior and potential security breaches. Furthermore, the exploitation technique falls under MITRE ATT&CK tactic T1203, specifically referencing exploit for client-side execution, where attackers leverage vulnerabilities in applications running on end-user systems to achieve initial access or privilege escalation. Understanding these mappings helps cybersecurity professionals categorize the risk accurately within broader threat intelligence frameworks and prioritize remediation efforts based on industry-standard classifications of software weaknesses and adversary behaviors.