CVE-2016-7051 in XmlMapper in the Data format Extension
Summary
by MITRE
XmlMapper in the Data format extension for Jackson (aka jackson-dataformat-xml) allows remote attackers to conduct server-side request forgery (SSRF) attacks via vectors related to a DTD.
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Analysis
by VulDB Data Team • 08/31/2020
The vulnerability identified as CVE-2016-7051 resides within the XmlMapper component of Jackson's Data Format extension, specifically exposing a server-side request forgery (SSRF) attack vector through improper handling of Document Type Definitions (DTDs). This flaw affects applications that process XML data using the Jackson library, creating a potential pathway for attackers to manipulate the underlying system's network requests. The vulnerability stems from the library's insufficient validation of external entities and DTD references during XML parsing operations, allowing malicious input to trigger unintended network communications.
The technical implementation of this vulnerability occurs when the XmlMapper processes XML documents containing external DTD references or entity declarations that point to external resources. When the parser encounters these references, it attempts to resolve them by making network requests to the specified locations without proper validation or restriction. This behavior creates an attack surface where remote adversaries can craft malicious XML payloads that force the application server to make unintended connections to internal or external systems, potentially exposing sensitive network resources or bypassing firewall restrictions. The flaw is particularly dangerous because it operates at the parsing layer, meaning it can be exploited through any application that utilizes Jackson's XML processing capabilities without proper input sanitization.
From an operational perspective, this vulnerability presents significant risks to enterprise environments where applications process untrusted XML data from external sources. Attackers can leverage this flaw to perform reconnaissance activities by probing internal network services, access restricted resources, or even establish command and control channels through the compromised application. The impact extends beyond simple information disclosure, as successful exploitation could lead to privilege escalation, lateral movement within the network, or the compromise of additional systems that are normally protected by network segmentation. Organizations using Jackson-based applications for processing XML data from untrusted sources face potential exposure to these attacks, particularly in environments where network access controls are insufficient or where applications operate with elevated privileges.
Security mitigations for CVE-2016-7051 primarily focus on updating the affected Jackson library components to versions that address the SSRF vulnerability through proper DTD handling and entity validation. Organizations should implement strict input validation and sanitization measures for all XML data processing operations, particularly when dealing with external or untrusted inputs. Network-level protections such as firewall rules and proxy configurations can help restrict outbound connections from affected applications, while application-level controls should disable external entity resolution and DTD processing entirely. The vulnerability aligns with CWE-611 (Improper Restriction of XML External Entity Reference) and maps to ATT&CK technique T1071.004 (Application Layer Protocol: XML External Entity) in the enterprise attack framework, emphasizing the need for comprehensive defense-in-depth strategies that address both the immediate vulnerability and broader security posture considerations.