CVE-2021-30485 in ezXML
Summary
by MITRE • 04/11/2021
An issue was discovered in libezxml.a in ezXML 0.8.6. The function ezxml_internal_dtd(), while parsing a crafted XML file, performs incorrect memory handling, leading to a NULL pointer dereference while running strcmp() on a NULL pointer.
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Analysis
by VulDB Data Team • 04/15/2021
The vulnerability identified as CVE-2021-30485 resides within the ezXML library version 0.8.6, specifically within the libezxml.a component. This issue manifests through the ezxml_internal_dtd() function which processes XML documents containing maliciously crafted input. The flaw represents a classic memory management error that occurs during the parsing of structured markup language files, creating a dangerous condition where the application attempts to dereference a null pointer during string comparison operations. Such vulnerabilities are particularly concerning in security contexts as they can lead to application crashes or potentially more severe exploitation scenarios.
The technical root cause of this vulnerability stems from improper memory handling within the XML parsing routine. When the ezxml_internal_dtd() function encounters a specially crafted XML file, it fails to properly validate or initialize memory pointers before invoking strcmp() operations. This results in a NULL pointer dereference condition where the strcmp() function attempts to compare strings using a null reference, causing the application to terminate unexpectedly or behave unpredictably. The vulnerability falls under the category of improper handling of memory allocation and deallocation patterns, which aligns with CWE-476, specifically addressing NULL pointer dereference issues in software implementations.
From an operational impact perspective, this vulnerability presents significant risks to systems relying on ezXML for XML processing tasks. Applications utilizing this library may experience unexpected crashes when processing untrusted XML input, leading to denial of service conditions that can disrupt business operations. The vulnerability is particularly dangerous in web applications, enterprise systems, and any software that processes external XML data feeds, as attackers could craft malicious XML documents to trigger the NULL pointer dereference and cause system instability. This represents a medium to high severity threat in environments where XML processing is a core functionality.
The exploitation of this vulnerability requires an attacker to provide a crafted XML file that triggers the specific parsing path within ezxml_internal_dtd(). This typically involves creating XML content with malformed DTD (Document Type Definition) declarations that cause the library to enter the problematic code path. The vulnerability aligns with ATT&CK technique T1211, which involves exploitation of memory corruption vulnerabilities, and demonstrates how seemingly benign input processing can lead to system instability. Organizations should consider this vulnerability as part of their broader security posture assessment, particularly in systems that process external XML data without proper input validation mechanisms.
Mitigation strategies for CVE-2021-30485 should prioritize updating to a patched version of the ezXML library where the memory handling issues have been resolved. System administrators should implement comprehensive input validation measures that filter or sanitize XML content before processing, reducing the attack surface for this particular vulnerability. Additionally, deploying network-based intrusion detection systems that can identify suspicious XML traffic patterns may help detect potential exploitation attempts. Organizations should also consider implementing application-level sandboxing or containerization techniques to limit the impact of potential exploitation. The fix typically involves proper initialization of memory pointers and validation checks before string comparison operations, ensuring that strcmp() is never invoked with NULL parameters, which directly addresses the fundamental memory handling flaw that causes the vulnerability.