CVE-2016-4434 in Tika
Summary
by MITRE
Apache Tika before 1.13 does not properly initialize the XML parser or choose handlers, which might allow remote attackers to conduct XML External Entity (XXE) attacks via vectors involving (1) spreadsheets in OOXML files and (2) XMP metadata in PDF and other file formats, a related issue to CVE-2016-2175.
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Analysis
by VulDB Data Team • 12/30/2022
Apache Tika version 1.13 and earlier contains a critical vulnerability in its XML processing implementation that exposes systems to XML External Entity attacks. This flaw stems from improper initialization of XML parsers and inadequate handler selection mechanisms within the library's document processing framework. The vulnerability affects multiple file format parsers including those handling OOXML spreadsheets and XMP metadata in PDF documents, creating multiple attack vectors for remote threat actors. The XXE vulnerability allows attackers to inject external entity references into XML documents processed by Tika, potentially enabling them to access local files, perform server-side request forgery attacks, or conduct denial of service operations against the affected system.
The technical implementation flaw resides in Tika's XML parser configuration where default settings fail to disable external entity resolution and do not properly validate or sanitize XML input streams. This misconfiguration occurs during the processing of structured document formats that embed XML content within their metadata or structural elements. When Tika encounters OOXML spreadsheet files, it processes embedded XML elements without proper security controls, and similarly when parsing PDF files with XMP metadata, the library fails to restrict external entity references in the XML processing pipeline. This vulnerability directly maps to CWE-611 (Improper Restriction of XML External Entity Reference) and represents a variant of the broader XXE attack pattern documented in the ATT&CK framework under technique T1213.1001 (Data from Information Repositories) and T1213.001 (Data from Information Repositories).
The operational impact of this vulnerability extends across organizations using Apache Tika for document processing, content management, or file analysis systems. Attackers can exploit this weakness by uploading maliciously crafted documents that contain XXE payloads, potentially gaining unauthorized access to internal system resources, exfiltrating sensitive data, or disrupting service availability. The vulnerability affects both direct exploitation scenarios where users upload documents and indirect attacks through automated processing pipelines that analyze incoming files. Organizations relying on Tika for security scanning, document conversion, or content extraction services face significant risk exposure, particularly in environments where untrusted documents are processed without proper input validation.
Mitigation strategies for CVE-2016-4434 require immediate patching of Apache Tika to version 1.13 or later where the XML parser initialization issues have been resolved. Organizations should also implement additional defensive measures including disabling external entity resolution in XML processing libraries, implementing strict input validation for document formats, and configuring network firewalls to restrict access to internal resources from processing systems. Security teams should conduct comprehensive vulnerability assessments to identify all systems using affected Tika versions and ensure proper configuration of XML parsers to disable external entity references. The remediation process should include updating all dependent applications and services that utilize Tika for document processing, as well as implementing monitoring controls to detect potential exploitation attempts. Additionally, organizations should consider implementing web application firewalls or API gateways that can filter out suspicious XML content before it reaches the Tika processing engine, providing an additional layer of defense against XXE attacks targeting this specific vulnerability.