CVE-2016-1838 in iOS
Summary
by MITRE
The xmlPArserPrintFileContextInternal 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 cause a denial of service (heap-based buffer over-read) via a crafted XML document.
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Analysis
by VulDB Data Team • 09/25/2024
The vulnerability identified as CVE-2016-1838 represents a critical heap-based buffer over-read flaw within the libxml2 library implementation. This issue specifically affects the xmlParserPrintFileContextInternal function which is responsible for handling XML document parsing operations. The vulnerability manifests when processing malformed XML content that has been carefully crafted to exploit memory access boundaries. The flaw exists in versions of libxml2 prior to 2.9.4 and has widespread impact across multiple Apple operating systems including iOS, macOS, tvOS, and watchOS. The vulnerability classification aligns with CWE-125, which describes out-of-bounds read conditions that occur when a program reads memory beyond the boundaries of a buffer. This particular implementation vulnerability demonstrates how XML parsing libraries can become attack vectors when proper input validation and memory boundary checking are absent.
The technical exploitation of this vulnerability occurs through the manipulation of XML document structures to trigger an improper memory access pattern. When a malicious XML document is processed by the affected libxml2 version, the xmlParserPrintFileContextInternal function attempts to read memory locations beyond the allocated buffer boundaries. This heap-based buffer over-read creates a situation where the parser accesses uninitialized memory or memory belonging to other data structures, potentially leading to application crashes or system instability. The attack vector is remote and requires no authentication, making it particularly dangerous for web applications and services that process untrusted XML input. This behavior corresponds to ATT&CK technique T1203, which involves the exploitation of memory corruption vulnerabilities to achieve system compromise.
The operational impact of CVE-2016-1838 extends beyond simple denial of service conditions, as heap corruption can potentially lead to more severe consequences including arbitrary code execution. In the context of Apple's ecosystem, this vulnerability affected major operating system versions where libxml2 is extensively used for parsing configuration files, web content, and various system components. The vulnerability affects not only user applications but also system-level processes that rely on XML parsing functionality. The specific versions impacted include iOS before 9.3.2, macOS before 10.11.5, tvOS before 9.2.1, and watchOS before 2.2.1, representing a broad range of Apple devices and operating system variants. Organizations and users running these vulnerable versions face significant risk when processing untrusted XML content, as the vulnerability can be exploited through web browsers, email clients, or any application that utilizes the affected XML parsing libraries. The remediation requires updating to libxml2 version 2.9.4 or later, which includes proper bounds checking and memory access validation to prevent the over-read condition from occurring during XML document processing.