CVE-2016-1835 in iOS
Summary
by MITRE
libxml2, as used in Apple iOS before 9.3.2 and OS X before 10.11.5, 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-2016-1835 represents a critical memory corruption flaw within libxml2, a widely deployed XML parsing library that forms a fundamental component of Apple's iOS and macOS operating systems. This vulnerability exists in versions of libxml2 prior to 2016, specifically affecting Apple iOS versions before 9.3.2 and macOS versions before 10.11.5. The flaw stems from inadequate input validation and memory management within the XML processing routines, creating a pathway for malicious actors to exploit the library's handling of malformed XML data. The vulnerability's impact extends beyond simple parsing errors, as it can be leveraged to achieve arbitrary code execution on affected systems, making it particularly dangerous in threat scenarios where remote code execution is the primary objective.
The technical exploitation of CVE-2016-1835 involves crafting a specially designed XML document that triggers memory corruption when processed by the vulnerable libxml2 library. This typically occurs through buffer overflows, use-after-free conditions, or other memory management errors that arise during XML parsing operations. The flaw manifests when the library attempts to parse malformed XML structures that cause it to write beyond allocated memory boundaries or access freed memory regions. Such memory corruption can lead to unpredictable behavior, application crashes, or more severely, provide attackers with the opportunity to inject and execute malicious code within the context of the vulnerable application. The vulnerability's classification aligns with CWE-121, which addresses stack-based buffer overflow conditions, and CWE-122, which covers heap-based buffer overflow scenarios, both of which are common in XML parsing libraries due to their complex memory management requirements.
The operational impact of this vulnerability is substantial, particularly in enterprise and mobile environments where Apple devices are prevalent. Attackers can leverage this flaw remotely to compromise iOS and macOS systems without requiring user interaction or elevated privileges, making it especially dangerous for targeted attacks. The vulnerability enables threat actors to perform various malicious activities including data exfiltration, system reconnaissance, privilege escalation, and persistent access to compromised systems. In the context of the MITRE ATT&CK framework, this vulnerability maps to techniques such as T1059 for command and scripting interpreter and T1068 for exploit for privilege escalation. The memory corruption nature of the flaw also aligns with ATT&CK technique T1070 for indicator removal on host, as compromised systems may be used to establish persistent backdoors and hide malicious activities.
Organizations and system administrators should prioritize immediate patching of affected systems to mitigate this vulnerability, as the window for exploitation remains open in unpatched environments. Apple released security updates for iOS 9.3.2 and macOS 10.11.5 that address the memory corruption issues within libxml2. Additional mitigations include implementing network segmentation, deploying XML filtering mechanisms, and monitoring for suspicious XML processing activities. Security teams should also consider implementing endpoint detection and response solutions that can identify anomalous XML parsing behavior or memory access patterns that may indicate exploitation attempts. The vulnerability underscores the importance of maintaining up-to-date third-party libraries and components, as libxml2's widespread use across various applications and operating systems makes it a prime target for attackers seeking to leverage memory corruption flaws for system compromise.