CVE-2015-7942 in iOS
Summary
by MITRE
The xmlParseConditionalSections function in parser.c in libxml2 does not properly skip intermediary entities when it stops parsing invalid input, which allows context-dependent attackers to cause a denial of service (out-of-bounds read and crash) via crafted XML data, a different vulnerability than CVE-2015-7941.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 07/11/2022
The vulnerability identified as CVE-2015-7942 affects the libxml2 library, specifically within the xmlParseConditionalSections function located in parser.c. This flaw represents a critical denial of service vulnerability that stems from improper handling of intermediary entities during XML parsing operations. The issue occurs when the parser encounters invalid input and fails to correctly skip over intermediate entities, leading to unpredictable behavior that can result in out-of-bounds memory reads and subsequent system crashes. This vulnerability operates within the context of XML processing applications that utilize libxml2 as their underlying parsing engine, making it particularly dangerous for web applications, XML-based services, and any system that processes external XML data from untrusted sources.
The technical implementation of this vulnerability resides in the xmlParseConditionalSections function which is responsible for parsing conditional sections within XML documents. When parsing encounters malformed XML data containing invalid conditional sections, the function does not properly advance the parser state to skip intermediary entities that should normally be bypassed during error recovery. This improper entity skipping mechanism leads to the parser attempting to access memory locations beyond the intended boundaries of the input data structure. The out-of-bounds read occurs because the parser continues to reference memory locations that were not properly validated or skipped, ultimately causing the application to crash or behave unpredictably. This behavior is classified as a memory corruption vulnerability that can be exploited through carefully crafted XML payloads designed to trigger the specific parsing path where the flaw exists.
From an operational impact perspective, CVE-2015-7942 presents a significant threat to systems that process XML data from external sources, including web applications, content management systems, and enterprise services that rely on XML parsing for data exchange. Attackers can exploit this vulnerability by constructing malicious XML documents that trigger the specific parsing scenario where intermediary entities are not properly skipped, resulting in system crashes that can be leveraged for denial of service attacks. The vulnerability's context-dependent nature means that exploitation requires specific conditions related to the XML structure and parsing state, but once triggered, it can cause complete application failure or system instability. The impact extends beyond simple service disruption to potentially compromise the availability of critical business systems that depend on XML processing capabilities.
Security professionals should prioritize patching affected systems as soon as possible, since the vulnerability can be exploited remotely without requiring authentication or special privileges. The recommended mitigation strategy involves upgrading to libxml2 versions that contain the fix for this specific parsing flaw, typically those released after the vulnerability disclosure. Organizations should also implement input validation and sanitization measures to filter potentially malicious XML data before it reaches the parsing layer, though this approach is considered a workaround rather than a complete solution. The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. Additionally, implementing proper XML schema validation and using secure parsing configurations can help reduce the attack surface, while monitoring for unusual parsing behavior or system crashes can aid in early detection of exploitation attempts.