CVE-2026-118017 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the SVG component. This vulnerability was fixed in Firefox 159.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical memory management error within the Scalable Vector Graphics rendering engine of Mozilla Firefox, specifically classified as an use-after-free condition. In software architecture, particularly in complex browsers handling rich media content like SVGs, objects are dynamically allocated and deallocated based on user interaction or document structure changes. A use-after-free flaw occurs when a program continues to use a pointer after the memory it points to has been freed. This typically happens due to logic errors where references to an object are not properly invalidated upon its destruction, leading to dangling pointers that still hold valid addresses but point to deallocated heap space. In the context of SVG processing, this often involves complex DOM manipulation or style updates where internal structures representing graphical elements may be removed from memory while other parts of the rendering pipeline retain references to them for further operations such as layout recalculation or painting.
The technical severity of this vulnerability lies in its potential for arbitrary code execution with the privileges of the target process. When an attacker can trigger a use-after-free condition, they gain control over how the freed memory is interpreted by subsequent instructions. By carefully crafting malicious SVG content that forces specific allocation and deallocation patterns, an adversary can manipulate the heap layout to place controlled data in the location previously occupied by the freed object. This allows for exploitation techniques such as type confusion or arbitrary read-write primitives, which are foundational steps in building a full exploit chain. The vulnerability was addressed in Firefox version 159 through rigorous code review and patching that ensures all references to SVG-related objects are properly nullified or updated when those objects are destroyed, thereby preventing access to invalid memory regions.
From an operational impact perspective, this flaw poses significant risks to end-users browsing untrusted web content. Successful exploitation could allow a remote attacker to execute arbitrary code on the victim's machine, potentially leading to full system compromise if combined with other vulnerabilities or insufficient sandboxing boundaries. The attack vector is primarily network-based, requiring only that a user visits a maliciously crafted webpage containing the exploit payload. This makes it particularly dangerous in scenarios involving phishing campaigns or compromised websites where users may inadvertently trigger the vulnerability by simply loading the page. The impact extends beyond immediate code execution to include potential data exfiltration, installation of malware, and lateral movement within networked environments if browser isolation mechanisms are bypassed.
Mitigation strategies for this vulnerability primarily involve ensuring that all Firefox installations are updated to version 159 or later as soon as possible. For organizations managing large fleets of endpoints, automated patch management systems should be configured to prioritize security updates related to the Gecko rendering engine. Additionally, users can reduce their exposure by employing browser hardening techniques such as disabling JavaScript on untrusted sites using extensions like NoScript or configuring strict content security policies if they are developers testing web applications. Security awareness training is also crucial to help users recognize and avoid suspicious links that might lead to pages containing malicious SVG payloads.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-416, which defines use-after-free errors as a distinct class of software weaknesses resulting from improper memory management practices. In the context of the MITRE ATT&CK framework, this flaw facilitates techniques associated with Initial Access and Execution, specifically leveraging client-side rendering engines to achieve code execution without user interaction beyond visiting the page. The exploitation path often involves heap spraying or precise allocation control, which falls under adversary behavior related to resource manipulation for privilege escalation or sandbox escape. Understanding these mappings helps security teams prioritize remediation efforts based on standardized threat intelligence frameworks and industry best practices for mitigating memory corruption vulnerabilities in web browsers.