CVE-2016-2175 in PDFbox
Summary
by MITRE
Apache PDFBox before 1.8.12 and 2.x before 2.0.1 does not properly initialize the XML parsers, which allows context-dependent attackers to conduct XML External Entity (XXE) attacks via a crafted PDF.
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Analysis
by VulDB Data Team • 10/11/2024
Apache PDFBox versions prior to 1.8.12 and 2.x prior to 2.0.1 contain a critical vulnerability that stems from improper XML parser initialization within the library's processing mechanisms. This flaw creates an exploitable condition where malicious actors can inject malicious XML entities into PDF documents, allowing them to leverage XML External Entity processing vulnerabilities. The vulnerability manifests when the PDFBox library processes PDF files that contain embedded XML content, particularly in the context of PDF forms or metadata sections where XML parsing occurs. The root cause lies in the library's failure to configure XML parsers with proper security restrictions, specifically the absence of disabling external entity resolution and external DTD loading. This weakness falls under the CWE-611 vulnerability category, which specifically addresses Improper Restriction of XML External Entity Reference, and aligns with the ATT&CK technique T1213.002 for Data from Information Repositories.
The operational impact of this vulnerability extends beyond simple information disclosure, as attackers can leverage XXE attacks to perform various malicious activities including server-side request forgery, internal network reconnaissance, and potentially unauthorized data access. When a vulnerable PDFBox application processes a maliciously crafted PDF file, the XML parser attempts to resolve external entities, which can lead to unintended network connections to attacker-controlled servers. The vulnerability is context-dependent because it requires a PDF file with embedded XML content to be processed by an application using the vulnerable PDFBox library, making it particularly dangerous in environments where users can upload or receive PDF documents from untrusted sources. This attack vector can be particularly devastating in enterprise environments where PDF processing is automated or where users frequently interact with PDF documents from external sources.
Mitigation strategies for this vulnerability require immediate patching of affected PDFBox versions to the recommended secure releases, specifically upgrading to PDFBox 1.8.12 or 2.0.1 and later versions. Organizations should also implement additional security controls including network segmentation to prevent unauthorized external connections, firewall rules to block outbound connections from PDF processing applications, and strict input validation for all PDF documents. The security configuration of XML parsers should be reviewed and hardened to ensure that external entity resolution is disabled, and that DTD loading is restricted. Security teams should also consider implementing automated scanning solutions that can detect and quarantine potentially malicious PDF files before they are processed by vulnerable applications. Regular security assessments and vulnerability scanning should be conducted to identify any applications still using vulnerable versions of PDFBox, as well as to ensure that proper security configurations are maintained across all PDF processing environments.