CVE-2015-8035 in iOS
Summary
by MITRE
The xz_decomp function in xzlib.c in libxml2 2.9.1 does not properly detect compression errors, which allows context-dependent attackers to cause a denial of service (process hang) via crafted XML data.
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Analysis
by VulDB Data Team • 07/11/2022
The vulnerability identified as CVE-2015-8035 resides within the libxml2 library version 2.9.1, specifically within the xz_decomp function located in xzlib.c. This flaw represents a critical issue in XML processing that can be exploited to cause denial of service conditions. The vulnerability stems from inadequate error detection mechanisms during decompression operations, particularly when handling xz-compressed data within XML documents. When maliciously crafted XML data containing malformed xz compression streams is processed by affected applications, the decompression function fails to properly identify compression errors and instead enters an infinite loop or prolonged hanging state.
This vulnerability operates under context-dependent conditions where the attacker must craft specific XML content that triggers the problematic decompression path. The technical flaw manifests as a lack of proper error handling in the xz decompression routine, which fails to validate compression stream integrity before attempting decompression. According to CWE classification, this represents a weakness in error handling and input validation, specifically categorized under CWE-248 Unchecked Return Value to NULL Pointer Dereference or CWE-399 Resource Management Errors. The flaw allows an attacker to craft XML documents that contain specially formatted xz-compressed data designed to trigger the decompression function's failure to detect malformed compression streams.
The operational impact of this vulnerability extends beyond simple denial of service, as it can affect any application that relies on libxml2 for XML processing and handles xz-compressed content. Systems processing untrusted XML data, including web applications, content management systems, and document processing services, become vulnerable to this attack vector. The vulnerability is particularly dangerous because it can cause complete process hang without any immediate crash or error reporting, making detection difficult and potentially allowing for prolonged service disruption. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 Network Denial of Service and T1210 Exploitation of Remote Services, as it enables attackers to consume system resources and cause service unavailability through crafted input processing.
Mitigation strategies for CVE-2015-8035 primarily involve upgrading to libxml2 version 2.9.2 or later, where the decompression error handling has been properly addressed. System administrators should also implement input validation measures to filter or sanitize XML content before processing, particularly when handling external or untrusted data sources. Additionally, application-level protections such as timeout mechanisms and resource limits can help prevent complete system hangs. Organizations should conduct thorough testing of XML processing components and monitor for any unusual processing patterns that might indicate exploitation attempts. The fix implemented in libxml2 2.9.2 includes enhanced error detection in the xz decompression function, ensuring that malformed compression streams properly terminate the decompression process rather than causing indefinite hanging states.