CVE-2021-39239 in Jena
Summary
by MITRE • 09/16/2021
A vulnerability in XML processing in Apache Jena, in versions up to 4.1.0, may allow an attacker to execute XML External Entities (XXE), including exposing the contents of local files to a remote server.
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Analysis
by VulDB Data Team • 09/19/2021
The vulnerability identified as CVE-2021-39239 represents a critical weakness in Apache Jena's XML processing capabilities that stems from inadequate input validation and secure XML parsing practices. This flaw exists within the software's handling of XML documents and specifically affects versions through 4.1.0, creating a pathway for malicious actors to exploit XML External Entity processing mechanisms. The vulnerability's classification under CWE-611 (Improper Restriction of XML External Entity Reference) indicates a fundamental failure in controlling external entity resolution during XML parsing operations. Attackers can leverage this weakness by crafting malicious XML payloads that reference external resources, potentially leading to unauthorized data exfiltration and system compromise.
The technical implementation of this vulnerability allows for arbitrary XML External Entity processing within Apache Jena's XML parsers, enabling attackers to reference external resources through various protocols including file access and network connections. When the vulnerable software processes XML documents containing external entity declarations, it fails to properly restrict or disable external entity resolution, creating opportunities for attackers to access local file systems and transmit sensitive data to remote servers. The flaw operates at the XML parser level, where default configurations permit external entity expansion without proper sanitization or restriction mechanisms. This type of vulnerability is particularly dangerous because it can be exploited through standard XML processing workflows without requiring special privileges or complex attack vectors.
The operational impact of CVE-2021-39239 extends beyond simple data exposure, as it provides attackers with potential access to sensitive information stored locally on systems running vulnerable Apache Jena instances. This includes configuration files, database credentials, system logs, and other potentially sensitive data that might be accessible through file protocol references in XML documents. The vulnerability can be exploited in various attack scenarios including server-side request forgery attacks, internal network reconnaissance, and data exfiltration operations. Organizations using Apache Jena for data processing, semantic web applications, or linked data services face significant risk exposure when running vulnerable versions, as the attack surface includes any system that processes XML input from untrusted sources. The vulnerability also aligns with ATT&CK technique T1071.004 (Application Layer Protocol: DNS) and T1566 (Phishing) as attackers might use this weakness in conjunction with other techniques to establish persistent access or escalate privileges.
Mitigation strategies for CVE-2021-39239 primarily involve upgrading to Apache Jena version 4.2.0 or later, which includes proper XML external entity restrictions and secure parsing configurations. Organizations should also implement XML parser hardening measures including disabling external entity resolution, restricting DTD processing, and implementing proper input validation for all XML processing operations. Security teams should conduct comprehensive vulnerability assessments to identify all systems running affected versions and ensure that XML processing configurations properly restrict external resource access. Additional defensive measures include network segmentation, monitoring for suspicious XML processing activities, and implementing web application firewalls that can detect and block malicious XML payloads. The vulnerability's remediation aligns with industry best practices for secure coding and XML processing as outlined in OWASP Top 10 2021 and NIST SP 800-125B guidelines for XML security. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security updates and maintain updated inventory of all Apache Jena installations across their infrastructure.