CVE-2019-20199 in ezXML
Summary
by MITRE
An issue was discovered in ezXML 0.8.3 through 0.8.6. The function ezxml_decode, while parsing a crafted XML file, performs incorrect memory handling, leading to NULL pointer dereference while running strlen() on a NULL pointer.
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Analysis
by VulDB Data Team • 03/05/2025
The vulnerability identified as CVE-2019-20199 affects ezXML library versions 0.8.3 through 0.8.6, representing a critical memory handling flaw that manifests during XML parsing operations. This issue resides within the ezxml_decode function which is responsible for processing and decoding XML content. The flaw occurs when the library encounters specifically crafted XML files that trigger improper memory management during the parsing sequence. The vulnerability is categorized under CWE-476 which specifically addresses NULL pointer dereference conditions, making it a direct implementation of this well-known weakness in software security practices.
The technical execution of this vulnerability involves the ezxml_decode function failing to properly validate or initialize memory pointers before attempting to perform string operations such as strlen(). When a maliciously constructed XML document is processed, the function attempts to call strlen() on a NULL pointer, causing the application to crash or potentially exhibit undefined behavior. This memory handling error stems from inadequate input validation and improper state management within the XML parsing routine. The flaw demonstrates a classic example of buffer overread conditions where the application accesses memory locations that have not been properly allocated or initialized, creating potential for denial of service attacks or in more severe cases, arbitrary code execution depending on the broader system context.
The operational impact of CVE-2019-20199 extends beyond simple application crashes, as it represents a fundamental flaw in how the ezXML library handles malformed input data. Systems utilizing affected versions of this library for XML processing are at risk of experiencing service disruption when encountering crafted XML payloads. The vulnerability can be exploited by attackers who craft malicious XML documents designed to trigger the NULL pointer dereference condition, potentially leading to system instability or complete application termination. This type of vulnerability is particularly dangerous in web applications and server environments where XML parsing is common, as it can be leveraged for denial of service attacks against critical infrastructure. The flaw also aligns with ATT&CK technique T1203 which involves exploiting weaknesses in software libraries to gain unauthorized access or disrupt system operations.
Mitigation strategies for this vulnerability require immediate patching of affected ezXML library versions to the latest releases that contain proper memory handling implementations. Organizations should implement comprehensive input validation measures and consider using more robust XML parsing libraries that have undergone security audits. The fix typically involves ensuring proper initialization of memory pointers before string operations and implementing defensive programming practices such as null checks and bounds validation. Additionally, system administrators should monitor for any applications that may be using vulnerable versions of ezXML and ensure all dependencies are updated to secure versions. This vulnerability serves as a reminder of the critical importance of proper memory management in security-critical code and the necessity of thorough testing with malformed inputs to identify potential NULL pointer dereference conditions.