CVE-2016-4658 in libxml2
Summary
by MITRE
libxml2 in Apple iOS before 10, OS X before 10.12, tvOS before 10, and watchOS before 3 allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted XML document.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2016-4658 represents a critical memory corruption flaw within Apple's libxml2 XML processing library that affected multiple Apple operating systems including iOS versions prior to 10, macOS versions before 10.12, tvOS versions before 10, and watchOS versions before 3. This vulnerability resides in the XML parser implementation and demonstrates the inherent risks associated with complex parsing libraries that handle untrusted input data. The flaw stems from improper memory management during XML document processing, creating opportunities for attackers to manipulate memory layout through carefully crafted malicious documents. According to CWE-125, this vulnerability falls under the category of out-of-bounds read conditions, where the parser fails to properly validate input boundaries during XML parsing operations. The impact extends beyond simple memory corruption as it provides adversaries with potential pathways for arbitrary code execution, making it particularly dangerous in environments where users might encounter untrusted XML content.
The technical exploitation of this vulnerability occurs when a malicious XML document is processed by the affected libxml2 library, triggering memory corruption that can be leveraged to execute arbitrary code or cause system crashes. Attackers can craft XML documents containing malformed elements, nested structures, or specific encoding sequences that cause the parser to access memory locations beyond allocated buffers. This memory corruption can manifest through various attack vectors including email attachments, web content, or file downloads that users might inadvertently process through Apple applications. The vulnerability's exploitation aligns with ATT&CK technique T1203, where adversaries leverage software vulnerabilities to gain code execution capabilities, and specifically maps to T1059 which involves the execution of commands through compromised applications. The parser's handling of XML entities, attribute processing, and namespace declarations creates multiple potential injection points where the memory corruption can be triggered, making this vulnerability particularly challenging to defend against.
The operational impact of CVE-2016-4658 extends beyond immediate system compromise to encompass broader security implications across Apple's ecosystem. Mobile devices running affected iOS versions, desktop systems with older macOS releases, and embedded systems like Apple TV and Watch devices all face potential compromise when processing untrusted XML content. The vulnerability's remote exploitation capability means that attackers can deliver malicious payloads through web-based attacks, email attachments, or compromised websites without requiring physical access to target devices. This makes the vulnerability particularly concerning for enterprise environments where users might encounter malicious XML content through various communication channels. The memory corruption can lead to system crashes, application instability, and potentially full system compromise when attackers successfully leverage the vulnerability to execute arbitrary code. Organizations should note that the vulnerability affects not just individual applications but the underlying XML processing infrastructure that many Apple applications depend upon, making the attack surface considerably broader than initially apparent. The security implications extend to data integrity and confidentiality, as successful exploitation could allow attackers to access sensitive information stored on affected devices or establish persistent access points for further attacks.
Mitigation strategies for CVE-2016-4658 should focus on immediate system updates and implementation of defensive measures. Apple released security updates for all affected operating systems that address the memory corruption issue through improved input validation and memory management within the libxml2 library. Organizations should prioritize deployment of these security patches across all affected systems, particularly in enterprise environments where users might encounter untrusted XML content. Network-based defenses can include XML content filtering and validation at perimeter devices, though this approach is less effective given the remote nature of the vulnerability. Application-level protections should focus on limiting XML processing to trusted sources and implementing input sanitization measures where possible. The vulnerability highlights the importance of keeping third-party libraries updated, as libxml2 is widely used across different platforms and applications beyond Apple's ecosystem. Security monitoring should include detection of unusual XML processing activities and potential exploitation attempts, with particular attention to malformed XML content being processed by affected systems. Additionally, user education about avoiding suspicious email attachments and web content can reduce the likelihood of successful exploitation, though this approach provides only partial protection given the remote nature of the vulnerability.