CVE-2016-1840 in iOS
Summary
by MITRE
Heap-based buffer overflow in the xmlFAParsePosCharGroup function in libxml2 before 2.9.4, as used in Apple iOS before 9.3.2, OS X before 10.11.5, tvOS before 9.2.1, and watchOS before 2.2.1, 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 • 08/21/2022
The vulnerability identified as CVE-2016-1840 represents a critical heap-based buffer overflow within the libxml2 library's xmlFAParsePosCharGroup function. This flaw exists in versions prior to 2.9.4 and affects multiple Apple operating systems including iOS, macOS, tvOS, and watchOS. The vulnerability stems from improper memory management during XML parsing operations, specifically when processing character groups within XML documents. Attackers can exploit this weakness by crafting malicious XML documents that trigger the buffer overflow condition, potentially leading to arbitrary code execution or system crashes. The issue demonstrates the classic characteristics of a heap overflow vulnerability where insufficient bounds checking allows data to be written beyond allocated memory boundaries, creating opportunities for memory corruption and exploitation.
The technical implementation of this vulnerability occurs within the xmlFAParsePosCharGroup function which handles the parsing of character groups in XML documents. When processing malformed XML input, the function fails to properly validate the size of data being written to heap-allocated buffers, resulting in a situation where attacker-controlled data can overwrite adjacent memory locations. This particular flaw falls under CWE-121 Heap-based Buffer Overflow, which is categorized as a memory safety issue affecting heap memory management. The vulnerability's exploitation potential is amplified by the fact that libxml2 is widely used across various systems and applications, making it an attractive target for attackers seeking to compromise multiple platforms simultaneously. The attack vector requires only a specially crafted XML document to be processed by an affected system, making it particularly dangerous for web applications and services that parse user-supplied XML content.
The operational impact of CVE-2016-1840 extends beyond simple denial of service scenarios to include full system compromise capabilities. When successfully exploited, attackers can achieve arbitrary code execution with the privileges of the affected application, potentially leading to complete system takeover. The vulnerability affects Apple's mobile and desktop operating systems, creating widespread exposure across consumer and enterprise environments. Systems running affected versions of iOS, macOS, tvOS, and watchOS are at risk when processing XML content from untrusted sources, including web applications, email attachments, or file downloads. The memory corruption resulting from this buffer overflow can be leveraged to manipulate program execution flow, potentially allowing attackers to inject malicious code or escalate privileges. This vulnerability represents a significant threat to organizations relying on Apple platforms, as it enables remote code execution without requiring user interaction beyond the simple act of processing the malicious XML content.
Mitigation strategies for CVE-2016-1840 primarily focus on updating affected systems to versions containing the patched libxml2 library. Apple released security updates for iOS 9.3.2, macOS 10.11.5, tvOS 9.2.1, and watchOS 2.2.1, which address the buffer overflow vulnerability. Organizations should prioritize patching affected systems and implementing network monitoring to detect potential exploitation attempts. Additional defensive measures include XML input validation and sanitization, restricting XML processing to trusted sources only, and implementing application-level restrictions on XML document size and complexity. The ATT&CK framework categorizes this vulnerability under T1203 Exploitation for Client Execution, as it enables attackers to execute malicious code through client-side XML processing. Network segmentation and web application firewalls can provide additional protection layers, while regular security assessments should verify that all systems are properly patched and that XML processing functions are adequately protected against malformed input. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates across all affected platforms.