CVE-2016-1963 in Firefox
Summary
by MITRE
The FileReader class in Mozilla Firefox before 45.0 allows local users to gain privileges or cause a denial of service (memory corruption) by changing a file during a FileReader API read operation.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability identified as CVE-2016-1963 resides within the FileReader class implementation in Mozilla Firefox versions prior to 45.0, representing a critical security flaw that could be exploited to escalate privileges or induce denial of service conditions. This issue manifests when local attackers manipulate files while they are being processed through the FileReader API, creating a race condition that leads to memory corruption. The vulnerability specifically affects the handling of file operations within the browser's JavaScript environment where applications can read file contents asynchronously through the FileReader interface. When a file is modified or deleted during an ongoing read operation, the browser's internal memory management fails to properly handle the concurrent access, resulting in unpredictable behavior that can be leveraged for privilege escalation or system instability.
The technical root cause of this vulnerability stems from inadequate synchronization mechanisms within the FileReader implementation, which fails to properly validate file states during read operations. This flaw aligns with CWE-367, a weakness category that encompasses time-of-check to time-of-use vulnerabilities, where the system checks a resource's state at one point and then uses that resource at a later point without revalidating the state. The race condition occurs between the file access check and the actual file reading operation, allowing an attacker to modify or remove the target file between these two phases. The memory corruption resulting from this race condition can manifest in various ways including heap corruption, stack corruption, or null pointer dereferences, all of which can lead to arbitrary code execution or complete browser crash. This vulnerability directly impacts the browser's security model by potentially allowing local users to bypass access controls and execute code with elevated privileges.
The operational impact of CVE-2016-1963 extends beyond simple denial of service scenarios, as it represents a significant threat to browser security and user privacy. Attackers could exploit this vulnerability to execute malicious code within the browser context, potentially leading to full system compromise if the browser has elevated privileges. The vulnerability is particularly dangerous in environments where users may be tricked into opening malicious files or where attackers can manipulate files in shared directories. From an attack perspective, this flaw aligns with techniques described in the MITRE ATT&CK framework under the T1059 category for command and scripting interpreter, where attackers could leverage the privilege escalation capabilities to gain deeper system access. The vulnerability affects all operating systems where Firefox is deployed, making it a widespread concern for organizations relying on the browser for web browsing activities. The memory corruption aspects of this vulnerability also make it particularly challenging to detect and prevent through traditional security measures, as the effects may not be immediately apparent and could manifest hours or days after exploitation.
Mitigation strategies for CVE-2016-1963 primarily focus on immediate patching of affected Firefox versions to 45.0 or later, where Mozilla implemented proper synchronization mechanisms to prevent the race condition. Organizations should also implement network segmentation and access controls to limit the potential impact of such vulnerabilities, while monitoring for suspicious file access patterns that might indicate exploitation attempts. Security teams should consider implementing browser hardening measures including disabling unnecessary JavaScript features, restricting file system access, and employing sandboxing techniques to limit the potential damage from successful exploits. The vulnerability underscores the importance of proper race condition handling in security-critical applications and highlights the necessity of thorough testing of concurrent access scenarios in web browsers. Additionally, organizations should maintain updated threat intelligence feeds to monitor for related exploitation attempts and ensure comprehensive incident response procedures are in place to address potential exploitation of this vulnerability.