CVE-2011-2821 in iOS
Summary
by MITRE
Double free vulnerability in libxml2, as used in Google Chrome before 13.0.782.215, allows remote attackers to cause a denial of service or possibly have unspecified other impact via a crafted XPath expression.
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Analysis
by VulDB Data Team • 04/13/2021
The CVE-2011-2821 vulnerability represents a critical double free condition within the libxml2 library implementation, which serves as a foundational XML parsing component utilized by numerous applications including Google Chrome. This flaw specifically manifests when processing crafted XPath expressions, creating a scenario where memory management functions execute the same free operation twice on the same memory block. The vulnerability stems from inadequate input validation and memory deallocation handling within the XPath evaluation subsystem of libxml2, where the parser fails to properly track memory references during complex XPath expression processing. The double free condition occurs when the XML parser encounters malformed XPath expressions that trigger specific code paths in the library's memory management routines, leading to the repeated deallocation of heap memory regions. This type of vulnerability falls under CWE-415, which categorizes improper deallocation of memory resources, and more specifically aligns with CWE-416, addressing the use of freed memory, though the double free aspect is more accurately described by CWE-415's broader scope. The vulnerability's exploitation potential extends beyond simple denial of service, as the memory corruption could potentially lead to arbitrary code execution depending on the system's memory layout and the attacker's ability to control the freed memory regions.
The operational impact of this vulnerability within Google Chrome's context is particularly severe given the browser's extensive use of XML parsing capabilities for various web standards and web application functionalities. When an attacker crafts a malicious XPath expression and injects it into a web page or web service response, the Chrome browser's rendering engine processes this through the vulnerable libxml2 library, triggering the double free condition. This scenario can result in immediate browser crashes and denial of service conditions, effectively preventing legitimate users from accessing web content. However, the potential for more severe consequences exists when considering that the memory corruption could be leveraged to execute arbitrary code, especially in environments where the freed memory is subsequently reallocated for different purposes. The vulnerability's exploitation requires a remote attacker to craft a specific XPath expression that triggers the memory management flaw, making it suitable for web-based attacks where malicious content can be delivered through standard web protocols. The attack vector aligns with ATT&CK technique T1059.007 for web-based command execution, though the actual exploitation requires the specific memory corruption conditions to be met.
Mitigation strategies for CVE-2011-2821 primarily focus on updating the affected libxml2 library to patched versions that implement proper memory management checks and input validation. Google Chrome users should immediately update to version 13.0.782.215 or later, which includes the necessary patches to address this vulnerability. System administrators and security teams should prioritize patching all systems that utilize vulnerable versions of libxml2, particularly those running web servers, applications, or services that process XML content with XPath expressions. The patching process should include verification that the updated library versions properly handle memory deallocation and that no other similar vulnerabilities exist within the XML processing stack. Additional defensive measures include implementing network-based intrusion detection systems that can identify and block malicious XPath expressions, as well as configuring web application firewalls to filter potentially harmful XML content. Organizations should also conduct comprehensive security assessments of their XML processing components to identify similar memory management flaws that might exist in other libraries or applications. The vulnerability underscores the importance of robust memory management practices in security-critical software components and highlights the necessity of thorough code review processes that examine memory allocation and deallocation patterns, particularly in libraries that handle untrusted input data. Regular security audits and penetration testing should include specific focus on memory management routines to prevent similar double free conditions from being introduced into software systems.