CVE-2016-2821 in Firefox
Summary
by MITRE
Use-after-free vulnerability in the mozilla::dom::Element class in Mozilla Firefox before 47.0 and Firefox ESR 45.x before 45.2, when contenteditable mode is enabled, allows remote attackers to execute arbitrary code or cause a denial of service (heap memory corruption) by triggering deletion of DOM elements that were created in the editor.
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Analysis
by VulDB Data Team • 10/23/2024
The vulnerability CVE-2016-2821 represents a critical use-after-free flaw within the mozilla::dom::Element class of Mozilla Firefox browsers. This security issue affects versions prior to Firefox 47.0 and Firefox ESR 45.x before 45.2, specifically when contenteditable mode is active. The flaw stems from improper memory management during the deletion process of DOM elements that are created within the editor environment, creating a scenario where freed memory can be accessed and manipulated by malicious actors.
The technical implementation of this vulnerability involves a classic use-after-free condition that occurs when the browser's DOM element management system fails to properly track the lifecycle of elements within contenteditable contexts. When a DOM element is deleted while still being referenced elsewhere in the browser's memory space, the system attempts to free the associated memory but continues to allow access to that memory location. This creates a race condition where attacker-controlled data can be written to the freed memory region, potentially leading to arbitrary code execution or system instability. The vulnerability specifically exploits the interaction between the DOM element deletion mechanism and the contenteditable functionality, which maintains references to elements even after they have been logically removed from the document structure.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to encompass full remote code execution capabilities. Attackers can leverage this flaw by crafting malicious web content that triggers the deletion of DOM elements within a contenteditable environment, subsequently manipulating the freed memory to inject and execute arbitrary code with the privileges of the browser process. This presents a significant risk to users who browse untrusted websites or encounter malicious content in email attachments or web applications that utilize contenteditable features. The heap memory corruption resulting from this vulnerability can lead to unpredictable behavior including crashes, data corruption, or complete system compromise depending on the exploitation method employed.
Mitigation strategies for CVE-2016-2821 primarily focus on immediate browser updates to patched versions, with users urged to upgrade to Firefox 47.0 or Firefox ESR 45.2 and later releases. Organizations should implement comprehensive patch management procedures to ensure all affected browser installations are updated promptly. Additional protective measures include disabling contenteditable functionality on untrusted websites when possible, implementing web application firewalls to monitor for suspicious DOM manipulation patterns, and employing sandboxing techniques to limit the potential impact of successful exploitation attempts. From a security standards perspective, this vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions, and maps to ATT&CK technique T1059.007 for execution through web browsers, emphasizing the need for layered defensive approaches including browser hardening, memory corruption defenses, and network-based monitoring solutions. The vulnerability demonstrates the critical importance of proper memory management in complex browser environments and highlights the necessity of thorough testing of DOM manipulation features, particularly those involving dynamic content editing scenarios.