CVE-2017-5946 in rubyzip Gem
Summary
by MITRE
The Zip::File component in the rubyzip gem before 1.2.1 for Ruby has a directory traversal vulnerability. If a site allows uploading of .zip files, an attacker can upload a malicious file that uses "../" pathname substrings to write arbitrary files to the filesystem.
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Analysis
by VulDB Data Team • 09/02/2020
The CVE-2017-5946 vulnerability represents a critical directory traversal flaw within the rubyzip gem version 1.2.0 and earlier, affecting Ruby applications that process untrusted zip file uploads. This vulnerability specifically targets the Zip::File component which is widely used for handling zip archives in Ruby web applications. The flaw allows malicious actors to exploit the lack of proper path validation during zip file extraction, enabling them to write files outside of the intended target directory. The vulnerability arises from insufficient input sanitization when processing zip archive entries that contain relative path traversal sequences such as "../" within their file paths. This issue directly impacts web applications that accept user-uploaded zip files for processing, particularly those implementing file upload functionalities without proper security controls.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious zip file containing entries with directory traversal sequences in their pathname components. During the extraction process, the rubyzip gem fails to properly validate or sanitize these paths, allowing the "../" sequences to navigate up the directory hierarchy and write files to arbitrary locations on the filesystem. This behavior violates fundamental security principles of file access control and can result in overwriting critical system files, injecting malicious code, or creating backdoor access points. The vulnerability is classified as a directory traversal attack pattern under CWE-22, which specifically addresses improper limitation of a pathname to a restricted directory. The flaw demonstrates a classic path normalization issue where the application fails to canonicalize or validate file paths before performing operations that could affect the filesystem.
The operational impact of CVE-2017-5946 extends beyond simple file overwrites to encompass potential complete system compromise when exploited in conjunction with other vulnerabilities or attack vectors. Web applications utilizing vulnerable rubyzip versions become susceptible to remote code execution if attackers can control the target directory where files are extracted, or if they can leverage the created files to establish persistent access. The vulnerability affects a broad range of Ruby applications including content management systems, file sharing platforms, backup utilities, and any service that processes untrusted zip archives. Attackers can leverage this flaw to escalate privileges, establish persistent backdoors, or gain unauthorized access to sensitive data stored on the affected systems. The vulnerability aligns with ATT&CK technique T1059.007 for execution through scripting and T1078 for valid accounts, as it can be used to create malicious files that persist on the system and potentially elevate privileges.
Mitigation strategies for CVE-2017-5946 require immediate remediation through upgrading the rubyzip gem to version 1.2.1 or later, which includes proper path validation and sanitization. Organizations should implement comprehensive input validation for all file upload operations, particularly for archive files, by canonicalizing paths and rejecting any entries containing traversal sequences. Additional defensive measures include restricting write permissions for application directories, implementing proper file path normalization before extraction, and employing sandboxing techniques to isolate file processing operations. Security monitoring should be enhanced to detect unusual file creation patterns or unauthorized file modifications in application directories. The vulnerability highlights the importance of dependency management and regular security updates, as well as the need for proper input validation at all levels of application processing. Organizations should also consider implementing web application firewalls and intrusion detection systems to monitor for exploitation attempts targeting this specific vulnerability pattern.