CVE-2017-6100 in tcpdf
Summary
by MITRE
tcpdf before 6.2.0 uploads files from the server generating PDF-files to an external FTP.
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Analysis
by VulDB Data Team • 08/16/2020
The vulnerability identified as CVE-2017-6100 affects TCPDF versions prior to 6.2.0, representing a critical security flaw in the popular PHP library used for generating PDF documents. This issue stems from improper input validation and insecure file handling mechanisms within the library's file upload functionality. The vulnerability allows malicious actors to exploit the PDF generation process to upload files from the server to an external File Transfer Protocol server, potentially compromising sensitive data and system integrity.
The technical flaw manifests when the TCPDF library processes certain PDF generation requests that include malicious file paths or references. The library fails to properly sanitize user inputs or validate file destinations, creating an opportunity for attackers to manipulate the upload process. This vulnerability specifically impacts the library's handling of external resources during PDF creation, where it may inadvertently transfer files from the server's file system to remote FTP servers without proper authorization checks. The flaw can be exploited through crafted PDF generation parameters that redirect the library's file handling to external destinations.
The operational impact of this vulnerability is severe and multifaceted, as it enables unauthorized data exfiltration from systems running vulnerable TCPDF versions. Attackers can leverage this flaw to extract sensitive files including configuration data, user information, application source code, and other confidential resources stored on the server. The vulnerability essentially provides a backdoor mechanism for data theft and can be particularly damaging in environments where PDF generation is frequently used for document processing, report generation, or user-facing applications. Organizations using vulnerable versions may experience significant data breaches, compliance violations, and potential system compromise.
Mitigation strategies for CVE-2017-6100 primarily involve immediate upgrade to TCPDF version 6.2.0 or later, which includes proper input validation and secure file handling mechanisms. System administrators should also implement network-level restrictions to prevent outbound FTP connections from web servers, particularly for the TCPDF library's file handling functions. Additional protective measures include implementing proper access controls, monitoring network traffic for suspicious FTP activity, and conducting regular security audits of PDF generation processes. The vulnerability aligns with CWE-22, which addresses improper limitation of a pathname to a restricted directory, and can be categorized under ATT&CK technique T1071.004 for application layer protocol usage. Organizations should also consider implementing web application firewalls and input validation controls to prevent exploitation of similar vulnerabilities in other components of their application stack.