CVE-2011-2834 in iOS
Summary
by MITRE
Double free vulnerability in libxml2, as used in Google Chrome before 14.0.835.163, allows remote attackers to cause a denial of service or possibly have unspecified other impact via vectors related to XPath handling.
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Analysis
by VulDB Data Team • 04/02/2017
The vulnerability identified as CVE-2011-2834 represents a critical double free condition within the libxml2 library implementation that was extensively utilized by Google Chrome browser versions prior to 14.0.835.163. This flaw resides in the XML parsing and XPath processing components of the library, specifically manifesting when the application handles malformed XML documents containing crafted XPath expressions. The double free vulnerability occurs when the same memory block is freed twice during the processing of XML data structures, creating a scenario where the memory management system becomes corrupted and potentially exploitable. Such conditions typically arise from improper error handling or memory allocation patterns within the library's internal processing routines that manage XPath evaluation contexts and associated data structures.
The technical exploitation of this vulnerability leverages the inherent memory management flaws within libxml2's XPath handling mechanisms, where the library fails to properly validate or sanitize XPath expressions before processing them through its internal evaluation engine. When Chrome processes malformed XML content containing specially crafted XPath queries, the underlying libxml2 parser enters an inconsistent state where memory blocks are deallocated multiple times, potentially leading to heap corruption. This condition can be triggered through various attack vectors including malicious web pages, XML documents embedded in web content, or crafted XML files delivered through network protocols. The vulnerability is particularly concerning because it operates at the core parsing layer of XML processing, affecting not only the browser's stability but potentially providing a pathway for more sophisticated attacks depending on the execution environment and memory layout.
The operational impact of CVE-2011-2834 extends beyond simple denial of service scenarios, as the double free condition creates opportunities for remote code execution or arbitrary code execution in certain circumstances. When the memory corruption occurs during heap operations, attackers can potentially manipulate the heap layout to redirect execution flow or inject malicious code into the browser process. The vulnerability affects a wide range of systems since libxml2 is a widely deployed XML parsing library used across numerous applications and platforms, making this flaw particularly dangerous in the context of web browsers where users frequently encounter untrusted XML content. The attack surface is significantly expanded due to the prevalence of XML processing in web applications, web services, and various content delivery mechanisms that Chrome encounters during normal browsing operations.
Mitigation strategies for CVE-2011-2834 primarily involve immediate patching of the affected Google Chrome versions and updating the underlying libxml2 library to patched versions that address the memory management issues in XPath processing. Organizations should prioritize updating their browser installations to versions 14.0.835.163 or later, which contain the necessary fixes for this vulnerability. Additionally, implementing network-level protections such as web application firewalls and content filtering systems can help reduce exposure by blocking suspicious XML content before it reaches vulnerable browser instances. The vulnerability aligns with CWE-415 which describes improper double free conditions, and could potentially map to ATT&CK techniques involving privilege escalation or code execution through memory corruption vulnerabilities. Security teams should also consider implementing runtime protections and memory safety monitoring to detect anomalous memory behavior that might indicate exploitation attempts. Regular security assessments of XML processing components and comprehensive testing of XPath expression handling should be part of ongoing security hygiene practices to prevent similar vulnerabilities from emerging in the future.
The remediation process requires careful attention to ensure that updates do not introduce compatibility issues with existing web applications or content that relies on specific XML parsing behaviors. Organizations should conduct thorough testing of their browser environments after applying patches to verify that legitimate web content continues to function properly while the vulnerability is neutralized. The vulnerability demonstrates the critical importance of proper memory management in security-critical libraries and underscores the need for rigorous code review processes that identify potential double free conditions in complex parsing and processing routines.