CVE-2019-14751 in Downloader
Summary
by MITRE
NLTK Downloader before 3.4.5 is vulnerable to a directory traversal, allowing attackers to write arbitrary files via a ../ (dot dot slash) in an NLTK package (ZIP archive) that is mishandled during extraction.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 12/01/2023
The NLTK Downloader vulnerability identified as CVE-2019-14751 represents a critical directory traversal flaw that affects versions prior to 3.4.5. This vulnerability specifically targets the extraction mechanism of NLTK packages contained within ZIP archives, creating a pathway for malicious actors to execute arbitrary file operations on systems where NLTK is installed. The flaw stems from inadequate input validation during the decompression process, allowing attackers to manipulate file paths through the use of ../ sequences that navigate outside the intended extraction directory. This directory traversal vulnerability falls under CWE-22, which categorizes path traversal attacks as a fundamental security weakness in software applications. The vulnerability is particularly concerning because NLTK is widely used in natural language processing applications and machine learning environments where it may be executed with elevated privileges or in contexts where arbitrary code execution could have severe consequences.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious NLTK package containing a ZIP archive with filenames that include ../ sequences during the package installation process. During extraction, the NLTK downloader fails to properly sanitize these paths, allowing the archive to be extracted to arbitrary locations on the filesystem. This misconfiguration enables attackers to overwrite critical system files, inject malicious code into existing applications, or create backdoor access points within the target environment. The vulnerability is particularly dangerous in automated deployment scenarios or when NLTK is used in web applications where user-supplied packages might be processed without proper security checks. The flaw demonstrates a classic lack of proper path validation and sanitization, which is a common pattern in software vulnerabilities and aligns with ATT&CK technique T1059.007 for executing malicious code through package managers or dependency installation tools.
The operational impact of CVE-2019-14751 extends beyond simple file overwrites, as it can lead to complete system compromise when NLTK is used in environments with elevated privileges or when attackers can influence package installation processes. Systems running vulnerable versions of NLTK are at risk of persistent backdoors being installed, critical infrastructure files being corrupted, or sensitive data being exposed through malicious file placement. The vulnerability is particularly dangerous in research environments, educational institutions, or enterprise settings where NLTK is commonly deployed for data science and artificial intelligence projects. Organizations using NLTK in automated pipelines or continuous integration systems may face supply chain compromises if malicious packages are introduced through trusted repositories. The vulnerability also affects cloud-based environments where NLTK might be used in serverless functions or containerized applications, potentially leading to broader infrastructure compromise. Security teams should consider this vulnerability as part of their threat modeling for machine learning and data science environments, as it can be exploited to gain unauthorized access to systems where NLTK is deployed.
The primary mitigation strategy involves upgrading to NLTK version 3.4.5 or later, which includes proper input validation and path sanitization during package extraction. Organizations should also implement strict package verification processes, including checksum validation and source authentication, before installing NLTK packages from untrusted sources. Network segmentation and access controls should be implemented to limit where NLTK can be executed, particularly in environments where it might be used to process untrusted input. Additionally, security monitoring should be enhanced to detect unusual file creation patterns or unauthorized modifications to system directories that might indicate exploitation attempts. Regular security audits of NLTK usage in automated environments and dependency management processes are essential to prevent exploitation. Organizations should also consider implementing application whitelisting or sandboxing mechanisms to restrict the capabilities of NLTK installations and limit the potential impact of any successful exploitation attempts. The vulnerability serves as a reminder of the importance of secure coding practices in dependency management systems and the need for thorough input validation in all file processing operations.