CVE-2016-4047 in OX AppSuite
Summary
by MITRE
An issue was discovered in Open-Xchange OX App Suite before 7.8.1-rev8. References to external Open XML document type definitions (.dtd resources) can be placed within .docx and .xslx files. Those resources were requested when parsing certain parts of the generated document. As a result an attacker can track access to a manipulated document. Usage of a document may get tracked and information about internal infrastructure may get exposed.
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Analysis
by VulDB Data Team • 10/08/2022
The vulnerability identified as CVE-2016-4047 affects Open-Xchange OX App Suite versions prior to 7.8.1-rev8, representing a significant security flaw in document processing capabilities. This issue stems from the application's improper handling of external references within Open XML document formats, specifically .docx and .xslx files, which are widely used for office document creation and sharing. The vulnerability allows attackers to embed malicious references to external Document Type Definition (DTD) resources within these documents, creating a mechanism for tracking user interactions and potentially exposing internal network infrastructure.
The technical flaw manifests when the OX App Suite processes documents containing external DTD references, particularly those that reference external resources during the parsing phase of document rendering. When users open or interact with manipulated documents, the application automatically attempts to fetch these external resources, creating network requests that can be monitored by attackers. This behavior creates a covert channel for tracking document access patterns, user activities, and potentially reveals internal network configurations through the network requests generated during the parsing process. The vulnerability operates at the application layer and leverages the XML parsing mechanisms that are standard in Open XML document processing, making it particularly insidious as it exploits legitimate document processing functionality.
The operational impact of this vulnerability extends beyond simple tracking capabilities, as it can provide attackers with valuable intelligence about internal infrastructure and user behavior patterns. When documents are opened within the OX App Suite environment, the automatic fetching of external DTD resources can reveal internal IP addresses, network configurations, and potentially sensitive information about the organization's network topology. This tracking capability can be exploited for reconnaissance purposes, allowing attackers to map network resources and identify potential targets for further exploitation. The vulnerability is particularly concerning in enterprise environments where sensitive documents are frequently shared and processed, as it can lead to information disclosure and provide attackers with insights into organizational network structures.
Organizations affected by this vulnerability should immediately implement mitigations including updating to OX App Suite version 7.8.1-rev8 or later, which contains the necessary patches to prevent external DTD resource fetching during document processing. Network administrators should also consider implementing network-level restrictions to prevent outbound connections to external resources when processing documents, particularly those originating from untrusted sources. Additional protective measures include configuring email filters to scan for documents containing external DTD references, implementing strict document validation policies, and establishing network monitoring to detect anomalous outbound requests from document processing applications. This vulnerability aligns with CWE-20: Improper Input Validation and can be categorized under ATT&CK technique T1071.004: Application Layer Protocol: DNS, as it exploits application-level protocols to establish covert communication channels. The vulnerability represents a classic example of how document processing applications can inadvertently create security exposure points through their handling of external references in structured documents.