CVE-2016-8739 in CXF
Summary
by MITRE
The JAX-RS module in Apache CXF prior to 3.0.12 and 3.1.x prior to 3.1.9 provides a number of Atom JAX-RS MessageBodyReaders. These readers use Apache Abdera Parser which expands XML entities by default which represents a major XXE risk.
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Analysis
by VulDB Data Team • 12/15/2022
The vulnerability identified as CVE-2016-8739 resides within the JAX-RS module of Apache CXF, specifically affecting versions prior to 3.0.12 and 3.1.x prior to 3.1.9. This security flaw manifests through the use of Atom JAX-RS MessageBodyReaders that leverage the Apache Abdera Parser for processing XML content. The core issue stems from the parser's default behavior of expanding XML entities during message processing, creating a significant XML External Entity (XXE) attack vector that could be exploited by malicious actors to gain unauthorized access to sensitive information or disrupt system operations.
The technical implementation of this vulnerability occurs when the JAX-RS module processes incoming Atom feed messages through the MessageBodyReader components. These readers utilize the Apache Abdera Parser library which, by default, enables entity expansion for XML documents. This configuration allows attackers to craft malicious XML payloads containing external entity references that, when processed, can cause the parser to retrieve and parse content from external resources. The vulnerability directly maps to CWE-611, which categorizes improper neutralization of external entity references in XML processing, and represents a classic XXE attack scenario where an attacker can leverage the parser's entity expansion capabilities to perform various malicious activities including data exfiltration, denial of service attacks, or internal network reconnaissance.
The operational impact of CVE-2016-8739 extends beyond simple data exposure, as it can enable attackers to perform server-side request forgery attacks and potentially gain access to internal system resources. When an application processes Atom feeds through the vulnerable JAX-RS module, an attacker can craft a malicious XML document that includes external entity declarations pointing to internal resources, local files, or even external servers controlled by the attacker. This creates opportunities for unauthorized data access, service disruption, and potential lateral movement within the network infrastructure. The vulnerability affects systems that process Atom feeds from untrusted sources, making it particularly dangerous in environments where such feeds are commonly received from external parties or where automated feed processing occurs without proper input validation.
Organizations can mitigate this vulnerability through several approaches that align with established security practices and frameworks. The primary mitigation involves upgrading to Apache CXF versions 3.0.12 or 3.1.9 and later, which disable entity expansion by default in the Abdera parser. Additionally, administrators should implement proper XML parsing configurations that explicitly disable external entity resolution and DTD processing. Security controls should include network segmentation to limit access to vulnerable systems, input validation and sanitization of all Atom feed content, and monitoring for suspicious XML processing activities. This remediation strategy addresses the core weakness identified in the ATT&CK framework under T1213, which covers data from information repositories, and aligns with the principle of least privilege by ensuring that XML parsers operate with minimal necessary permissions and access rights. The vulnerability demonstrates the critical importance of proper XML processing security controls and highlights the need for regular security updates and vulnerability assessments in enterprise software environments.