CVE-2020-29128 in petl
Summary
by MITRE • 11/26/2020
petl before 1.68, in some configurations, allows resolution of entities in an XML document.
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Analysis
by VulDB Data Team • 12/10/2020
The vulnerability identified as CVE-2020-29128 affects the petl library version 1.68 and earlier, representing a significant security flaw in XML entity resolution handling. This issue specifically manifests in certain configurations where the library fails to properly restrict XML entity expansion, creating potential pathways for malicious actors to exploit the system. The petl library serves as a data processing tool for python applications, commonly used for extracting, transforming, and loading data from various sources including structured formats like xml. When entities within xml documents are improperly resolved, this creates a vector for denial of service attacks and potentially remote code execution depending on the environment and implementation details.
The technical flaw stems from insufficient validation and restriction of external entity references within xml processing within the petl library. This vulnerability aligns with CWE-611, which specifically addresses improper restriction of XML external entities, a well-documented weakness in xml processing libraries. The issue occurs when the library processes xml documents that contain external entity declarations or references that can be resolved by the underlying xml parser. Without proper safeguards, an attacker can craft malicious xml content that includes entity references designed to cause excessive resource consumption or trigger unintended behavior in the processing environment. The vulnerability is particularly concerning because xml parsers typically resolve entities by fetching external resources, which can lead to resource exhaustion through entity expansion attacks or direct exploitation of the underlying xml processing mechanisms.
The operational impact of CVE-2020-29128 extends beyond simple denial of service scenarios, potentially enabling more sophisticated attacks depending on how the petl library is integrated into applications. Systems that process untrusted xml data through vulnerable petl versions become susceptible to xml external entity attacks, commonly known as XXE (XML External Entity) vulnerabilities. This can result in unauthorized data access, server-side request forgery, or resource exhaustion that disrupts normal service operations. The vulnerability is particularly dangerous in applications that process user-supplied xml data or integrate with web services that return xml responses, as these scenarios provide direct attack vectors. Organizations using petl in production environments may experience service degradation or complete system unavailability if attackers exploit this vulnerability effectively.
Mitigation strategies for CVE-2020-29128 focus primarily on upgrading to petl version 1.68 or later, which includes proper entity resolution controls and restrictions. Security teams should implement comprehensive input validation for all xml data processed through petl libraries, ensuring that xml documents are sanitized and that external entity references are properly disabled or restricted. Organizations should also consider implementing xml parser configurations that disable external entity resolution entirely, following security best practices recommended by organizations such as the Open Web Application Security Project. Additionally, network-level controls including firewalls and intrusion detection systems can help monitor for suspicious xml processing activities. The remediation process should include thorough testing of updated libraries to ensure compatibility with existing applications while maintaining security posture. Regular security assessments and vulnerability scanning should be implemented to identify any other instances of vulnerable petl usage within the organization's infrastructure, aligning with the ATT&CK framework's defense in depth principles for preventing and detecting such vulnerabilities in data processing systems.