CVE-2016-9063 in tvOS
Summary
by MITRE
An integer overflow during the parsing of XML using the Expat library. This vulnerability affects Firefox < 50.
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Analysis
by VulDB Data Team • 01/20/2021
The CVE-2016-9063 vulnerability represents a critical integer overflow flaw within the Expat XML parsing library that directly impacted Firefox versions prior to 50. This vulnerability stems from improper handling of integer values during XML document processing, creating a scenario where maliciously crafted XML content could trigger arithmetic overflow conditions. The flaw specifically manifests when the parser attempts to calculate memory allocation sizes based on parsed integer values, allowing an attacker to manipulate these calculations through crafted input data. The vulnerability is classified under CWE-190 as an integer overflow condition, which occurs when an operation on signed or unsigned integers exceeds the maximum value that can be represented by the data type, leading to unexpected behavior in the application's memory management. This type of vulnerability falls within the ATT&CK technique T1203 - Exploitation for Client Execution, as it enables attackers to execute arbitrary code through malformed XML content that could be embedded in web pages or documents.
The technical implementation of this vulnerability involves the Expat library's XML parser encountering XML elements with attributes or content that contain integer values which, when processed, result in integer overflow conditions. When the parser attempts to allocate memory for processing these values, the overflow causes the allocation size to become negative or excessively large, potentially leading to memory corruption or heap-based buffer overflows. The vulnerability is particularly dangerous because XML parsing is a common operation in web browsers, and attackers can leverage this flaw through malicious web content that triggers the vulnerable code path. The integer overflow occurs during the parsing phase when the library attempts to determine the size of memory allocations needed for processing XML content, specifically when handling large or malformed integer values in XML attributes or element content. This creates an opportunity for attackers to control memory allocation behavior and potentially execute arbitrary code with the privileges of the affected browser process.
The operational impact of CVE-2016-9063 is severe and far-reaching, as it enables remote code execution attacks against vulnerable Firefox installations. Attackers could craft malicious XML documents or web pages that, when processed by the affected browser, would trigger the integer overflow condition and potentially allow for arbitrary code execution. This vulnerability could be exploited through various attack vectors including malicious websites, email attachments, or any content that would cause Firefox to parse XML data. The exploitation typically involves crafting XML content with carefully manipulated integer values that cause the parser to allocate insufficient or excessive memory, leading to memory corruption that can be leveraged for privilege escalation or arbitrary code execution. The vulnerability affects not just individual user systems but also represents a significant risk to enterprise environments where Firefox is widely deployed, as it could be used to compromise user sessions, steal sensitive data, or establish persistent access to target systems. The integer overflow condition could also potentially lead to denial of service scenarios where the browser crashes or becomes unresponsive due to memory allocation failures.
Mitigation strategies for CVE-2016-9063 primarily focus on updating to patched versions of Firefox and ensuring that the underlying Expat library is properly updated. Users should immediately upgrade to Firefox version 50 or later, which includes patches addressing this vulnerability. System administrators should implement comprehensive patch management procedures to ensure all affected systems are updated promptly. Organizations should also consider implementing network-based protections such as web application firewalls that can detect and block malicious XML content before it reaches vulnerable browsers. Additional mitigations include configuring browser security settings to limit XML processing capabilities and implementing sandboxing mechanisms that can contain potential exploits. The vulnerability highlights the importance of proper input validation and integer overflow protection in XML parsers and other libraries that handle user-provided data. Security monitoring should include detection of unusual memory allocation patterns or XML parsing errors that might indicate exploitation attempts. Regular security assessments of web applications and browser configurations should be conducted to identify potential exposure to similar vulnerabilities in other XML processing components. The fix implemented in Firefox 50 and subsequent versions involved proper bounds checking and integer overflow protection mechanisms within the Expat library integration, ensuring that memory allocation calculations cannot be manipulated through crafted input data.