CVE-2021-33497 in transfer.sh
Summary
by MITRE • 05/24/2021
Dutchcoders transfer.sh before 1.2.4 allows Directory Traversal for deleting files.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 05/27/2021
The vulnerability identified as CVE-2021-33497 affects transfer.sh versions prior to 1.2.4, representing a critical directory traversal flaw that specifically targets file deletion operations within the Dutchcoders transfer.sh application. This vulnerability falls under the Common Weakness Enumeration category CWE-22, which defines improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. The flaw enables malicious actors to exploit the application's file deletion functionality by manipulating input parameters to access and remove files outside the intended directory structure, potentially compromising the entire file system.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the file deletion endpoint of transfer.sh. When users attempt to delete files through the application's interface, the system fails to properly validate or sanitize the file paths provided in the deletion requests. This allows attackers to craft malicious requests containing directory traversal sequences such as "../" or "..\", which can navigate outside the intended file storage directories. The vulnerability specifically impacts the deletion functionality rather than upload or download operations, making it particularly dangerous as it can be used to remove critical system files, configuration data, or user content from the server.
Operationally, this vulnerability presents significant risks to organizations relying on transfer.sh for file sharing services, as it can be exploited to perform unauthorized file deletion operations that may result in data loss, service disruption, or even system compromise. Attackers could potentially target sensitive files, log files, or configuration data stored on the same server, leading to complete system compromise or denial of service conditions. The impact extends beyond simple data loss, as this vulnerability could be leveraged as part of a broader attack chain where adversaries first gain access to the file system through directory traversal, then escalate privileges or execute additional malicious operations. The vulnerability also aligns with ATT&CK technique T1070.004, which covers "File Deletion" through the use of directory traversal to manipulate file system permissions and remove critical resources.
Organizations should immediately upgrade to transfer.sh version 1.2.4 or later to remediate this vulnerability, as the fix implements proper input validation and path sanitization measures that prevent directory traversal attempts during file deletion operations. Additional mitigations include implementing proper access controls, restricting file deletion capabilities to authorized users only, and monitoring deletion operations for suspicious activity. Network segmentation and firewall rules can help limit exposure by restricting access to the transfer.sh service to trusted networks only. Security teams should also implement logging and monitoring solutions that track file deletion operations, particularly those involving unusual file paths or patterns that may indicate directory traversal attempts. The vulnerability demonstrates the critical importance of input validation in web applications, particularly for operations that modify file system state, as even seemingly benign functions like file deletion can become attack vectors when proper security controls are not implemented.