CVE-2019-20198 in ezXML
Summary
by MITRE
An issue was discovered in ezXML 0.8.3 through 0.8.6. The function ezxml_ent_ok() mishandles recursion, leading to stack consumption for a crafted XML file.
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Analysis
by VulDB Data Team • 03/19/2024
The vulnerability identified as CVE-2019-20198 represents a critical stack consumption issue within the ezXML library version 0.8.3 through 0.8.6. This flaw resides in the ezxml_ent_ok() function which fails to properly manage recursive processing of XML entities, creating a potential denial of service condition that can be exploited through carefully crafted malicious XML input files. The vulnerability stems from insufficient recursion depth checking and improper stack management during XML entity processing, making it particularly dangerous in applications that process untrusted XML data.
The technical implementation of this vulnerability demonstrates a classic stack overflow condition where the ezxml_ent_ok() function does not adequately validate or limit recursive entity references within XML documents. When processing malformed XML containing deeply nested or circular entity references, the function continues to consume stack space without proper bounds checking, eventually exhausting available stack memory and causing application crashes or system instability. This behavior aligns with CWE-674, which specifically addresses uncontrolled recursion in software implementations. The flaw operates at the parsing level where XML entity expansion occurs, making it particularly insidious as it can be triggered through normal XML processing workflows without requiring special privileges or complex attack vectors.
From an operational impact perspective, this vulnerability poses significant risks to systems that rely on ezXML for XML processing, including web applications, middleware services, and enterprise software solutions. Attackers can craft malicious XML files that trigger the recursive processing behavior, leading to resource exhaustion and service disruption. The vulnerability affects any application that uses ezXML library versions within the affected range, potentially causing widespread denial of service conditions across multiple systems. According to ATT&CK framework, this vulnerability maps to T1499.004 - Network Denial of Service, as it enables adversaries to consume system resources and disrupt normal service operations. The impact extends beyond simple application crashes to potentially affect system availability and overall infrastructure stability, particularly in high-traffic environments where XML processing is frequent.
Mitigation strategies for CVE-2019-20198 should prioritize immediate patching of affected ezXML library versions to the latest stable releases that contain proper recursion depth controls. Organizations should implement XML input validation and sanitization measures, including setting reasonable limits on entity expansion and recursive reference depth. Network-level protections such as XML firewall rules and rate limiting can help reduce the impact of exploitation attempts. Additionally, monitoring systems should be configured to detect unusual resource consumption patterns that may indicate exploitation attempts. Security teams should also consider implementing application sandboxing and memory protection mechanisms to contain potential impacts. The vulnerability highlights the importance of proper input validation and resource management in XML parsers, emphasizing that recursive processing must always include appropriate safeguards against unbounded expansion. Organizations should conduct thorough vulnerability assessments to identify all systems using affected ezXML versions and ensure comprehensive remediation across their infrastructure.