CVE-2016-1762 in iOS
Summary
by MITRE
The xmlNextChar function in libxml2 before 2.9.4 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 • 12/18/2025
The xmlNextChar function in libxml2 versions prior to 2.9.4 contains a critical heap-based buffer over-read vulnerability that enables remote attackers to execute denial of service attacks through carefully crafted XML documents. This vulnerability resides within the XML parsing library's character processing mechanism, where insufficient bounds checking allows malicious input to traverse memory boundaries beyond allocated heap buffers. The flaw specifically manifests when the parser encounters malformed XML content that triggers the xmlNextChar function to read data from memory locations that extend beyond the intended buffer limits, creating a predictable pattern of memory access violations.
The technical implementation of this vulnerability stems from improper input validation within the libxml2 XML parser's character iteration logic. When processing XML documents containing specially constructed byte sequences, the xmlNextChar function fails to properly verify buffer boundaries before advancing character pointers, leading to memory reads that extend beyond allocated heap memory regions. This over-read condition can cause the application to access uninitialized memory or memory belonging to other data structures, resulting in unpredictable behavior and system instability. The vulnerability is particularly concerning because it operates entirely within the parsing layer without requiring any special privileges or complex exploitation techniques, making it accessible to attackers with minimal technical expertise.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential system instability and resource exhaustion. Remote attackers can craft malicious XML documents that, when processed by vulnerable applications, trigger the buffer over-read condition and cause applications to crash or become unresponsive. This denial of service condition affects any software that relies on libxml2 for XML processing, including web servers, application frameworks, database systems, and enterprise applications that handle XML data. The vulnerability's exploitation can lead to cascading failures in systems where XML processing is a core component, potentially affecting multiple services or entire application stacks that depend on the affected library.
Mitigation strategies for this vulnerability require immediate patching of affected libxml2 installations to version 2.9.4 or later, which includes proper bounds checking and memory boundary validation within the xmlNextChar function. Organizations should implement comprehensive patch management procedures to ensure all systems utilizing libxml2 are updated promptly, particularly in environments where XML processing is common. Additionally, input validation measures should be implemented at application layers to sanitize XML data before processing, though this represents a secondary defense since the primary fix must occur at the library level. Network segmentation and access controls can help limit exposure by restricting access to XML processing endpoints, while monitoring systems should be deployed to detect unusual patterns of XML processing that might indicate exploitation attempts. This vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and represents a classic example of memory safety issues commonly addressed through proper bounds checking and defensive programming practices. The ATT&CK framework categorizes this as a denial of service technique that leverages software vulnerabilities to disrupt system availability, with the specific technique mapping to T1499.004 for network denial of service and T1595.001 for reconnaissance through vulnerability scanning.