CVE-2015-8241 in libxml2
Summary
by MITRE
The xmlNextChar function in libxml2 2.9.2 does not properly check the state, which allows context-dependent attackers to cause a denial of service (heap-based buffer over-read and application crash) or obtain sensitive information via crafted XML data.
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Analysis
by VulDB Data Team • 07/01/2022
The xmlNextChar function in libxml2 version 2.9.2 contains a critical vulnerability that stems from inadequate state validation during XML parsing operations. This flaw resides within the core parsing logic that processes character sequences in XML documents, creating a pathway for malicious input to exploit improper state handling. The vulnerability manifests when the function fails to properly validate the parsing context before advancing through character data, leading to unpredictable behavior in the underlying memory management system. Such deficiencies in state checking represent a fundamental breakdown in input validation that can be leveraged by attackers to disrupt normal application operations. The issue impacts the XML parsing library's ability to maintain consistent internal state during document processing, creating opportunities for exploitation that extend beyond simple denial of service scenarios.
The technical implementation of this vulnerability allows attackers to craft specially formatted XML data that triggers the buffer over-read condition when the xmlNextChar function processes malformed character sequences. This heap-based buffer over-read occurs because the function advances memory pointers without sufficient bounds checking against the current parsing state, potentially causing the application to read beyond allocated memory boundaries. The flaw specifically affects how the parser handles character encoding transitions and state transitions between different XML elements, creating a scenario where memory corruption can occur during normal parsing operations. When malicious XML data is processed, the function's failure to validate state transitions results in memory access violations that can either crash the application or expose sensitive data from adjacent memory locations. This type of vulnerability aligns with CWE-129, which addresses improper validation of array indices and buffer overflows, and represents a classic example of how insufficient state management can lead to memory safety issues.
The operational impact of CVE-2015-8241 extends beyond simple application crashes to include potential information disclosure vulnerabilities that could expose sensitive system data. When exploited successfully, this vulnerability can cause applications using libxml2 to crash repeatedly, creating denial of service conditions that disrupt legitimate user access to services. The heap-based buffer over-read condition also presents opportunities for attackers to extract memory contents that may contain confidential information such as cryptographic keys, user credentials, or system configuration details. Organizations relying on applications that utilize libxml2 for XML processing are particularly vulnerable, including web applications, enterprise software platforms, and systems handling XML-based data interchange. The context-dependent nature of this vulnerability means that exploitation requires specific XML input patterns but can be automated once the attack vector is understood, making it a significant risk for applications processing untrusted XML data from external sources.
Mitigation strategies for this vulnerability should focus on immediate patching of affected libxml2 installations to version 2.9.3 or later, which contains the necessary state validation fixes. System administrators should conduct comprehensive vulnerability assessments to identify all applications and services that depend on libxml2, particularly those handling external XML input. Implementing input validation measures at application layers can provide additional protection by sanitizing XML data before it reaches the vulnerable parsing functions. Network segmentation and access controls should be enforced to limit exposure of systems that process XML data from untrusted sources. Regular security monitoring and intrusion detection systems should be configured to detect unusual application crash patterns or memory access violations that might indicate exploitation attempts. Organizations should also consider implementing application whitelisting policies and restricting XML parsing capabilities in applications where possible, following principles outlined in the attack mitigation framework that emphasize reducing attack surface and implementing defense-in-depth strategies. The vulnerability serves as a reminder of the critical importance of proper state management in security-critical libraries and the need for comprehensive testing of parsing functions against malformed input scenarios.