CVE-2019-20007 in ezXML
Summary
by MITRE
An issue was discovered in ezXML 0.8.2 through 0.8.6. The function ezxml_str2utf8, while parsing a crafted XML file, performs zero-length reallocation in ezxml.c, leading to returning a NULL pointer (in some compilers). After this, the function ezxml_parse_str does not check whether the s variable is not NULL in ezxml.c, leading to a NULL pointer dereference and crash (segmentation fault).
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Analysis
by VulDB Data Team • 03/17/2024
The vulnerability identified as CVE-2019-20007 represents a critical memory management flaw within the ezXML library version 0.8.2 through 0.8.6. This issue stems from improper handling of string conversion operations during XML parsing, specifically within the ezxml_str2utf8 function that processes character encoding transformations. The flaw manifests when the library encounters specially crafted XML input designed to trigger a zero-length reallocation scenario, a condition that can cause the function to return a NULL pointer under certain compiler environments. This particular behavior aligns with CWE-476 which addresses null pointer dereference vulnerabilities, and demonstrates how seemingly benign memory allocation operations can lead to system instability.
The operational impact of this vulnerability extends beyond simple crash conditions to potentially enable more sophisticated attack vectors. When ezxml_str2utf8 returns a NULL pointer due to the zero-length reallocation, the subsequent ezxml_parse_str function fails to validate this critical return value before attempting to use the s variable. This omission creates a direct path for null pointer dereference, resulting in segmentation faults that can terminate applications abruptly. The vulnerability affects any software system that relies on ezXML for XML processing, particularly those handling untrusted input from external sources. The segmentation fault condition can be exploited to cause denial of service attacks against applications, and in some scenarios could potentially be leveraged to execute arbitrary code if the application's memory management is further compromised.
The technical exploitation of CVE-2019-20007 requires attackers to craft XML documents that specifically trigger the zero-length reallocation path within ezxml_str2utf8 function. This attack vector is categorized under the ATT&CK technique T1203, which involves exploitation of memory corruption vulnerabilities to cause application crashes or system instability. The vulnerability's presence in multiple versions of ezXML indicates a persistent flaw in the library's string handling logic, suggesting that developers may have overlooked proper null pointer validation during the library's development lifecycle. Organizations utilizing ezXML in their applications should consider this vulnerability as a high-priority risk, particularly in systems where XML processing is a core functionality and where input validation is insufficient.
Mitigation strategies for CVE-2019-20007 primarily involve immediate software updates to versions of ezXML that address the memory management issue. System administrators should prioritize patching affected applications and libraries to prevent exploitation, as the vulnerability can be triggered through any XML input that causes the specific allocation path. Additionally, implementing proper input validation and sanitization measures can provide defense-in-depth protection, ensuring that XML documents are properly validated before being processed by ezXML functions. The vulnerability highlights the importance of comprehensive error handling in memory management operations and underscores the need for rigorous testing of edge cases, particularly those involving allocation scenarios that may result in zero-length operations. Organizations should also consider implementing runtime monitoring and intrusion detection systems to identify potential exploitation attempts targeting this class of memory corruption vulnerabilities.