CVE-2022-31533 in umbral
Summary
by MITRE • 07/11/2022
The decentraminds/umbral repository through 2020-01-15 on GitHub allows absolute path traversal because the Flask send_file function is used unsafely.
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Analysis
by VulDB Data Team • 07/20/2022
The vulnerability identified as CVE-2022-31533 resides within the decentraminds/umbral repository, a cryptographic library implementation that was active until January 15, 2020. This repository implements the Umbral proxy re-encryption scheme and was designed for secure data sharing and access control. The flaw manifests in how the Flask web framework's send_file function is utilized within the application's file serving mechanisms, creating a critical security weakness that allows unauthorized access to arbitrary files on the server. The vulnerability stems from improper input validation and sanitization of file paths that are passed to the Flask send_file function, which is designed to serve files from the filesystem to HTTP clients. When user-supplied input directly influences the file path parameter, attackers can manipulate this input to traverse the file system beyond the intended directory boundaries.
The technical implementation of this vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. The Flask send_file function, when used without proper path validation, accepts absolute paths or paths containing directory traversal sequences such as "../" or "..\\", allowing attackers to navigate the file system hierarchy. This weakness enables an attacker to access sensitive files that should remain protected, including configuration files, source code, database files, and potentially system files that contain credentials or other sensitive information. The vulnerability is particularly dangerous because it can be exploited through simple HTTP requests that manipulate the file path parameter, making it accessible to attackers with minimal technical expertise.
The operational impact of CVE-2022-31533 extends beyond simple data exposure to encompass potential system compromise and data breach scenarios. An attacker who successfully exploits this vulnerability can gain access to sensitive data that may include cryptographic keys, user credentials, application configuration files, and other confidential information stored on the server. The implications are severe for any application that relies on the umbral repository for secure data handling, as the vulnerability could lead to unauthorized access to encrypted data, compromise of cryptographic operations, and potential data exfiltration. The attack surface is particularly concerning because the vulnerable code may be present in production systems that handle sensitive information, making this a critical issue for organizations relying on this cryptographic framework.
Mitigation strategies for CVE-2022-31533 should focus on implementing proper input validation and sanitization of file paths before they are processed by the Flask send_file function. The recommended approach involves using a whitelist of allowed file paths or implementing strict path validation that ensures all file operations occur within a designated safe directory. Organizations should also consider implementing the principle of least privilege by running the application with minimal required permissions and ensuring that the application cannot access files outside of its intended scope. Additionally, the use of absolute paths with proper validation or relative paths within a controlled directory structure can prevent the exploitation of path traversal vulnerabilities. The ATT&CK framework categorizes this type of vulnerability under T1083 (File and Directory Discovery) and T1566 (Phishing with Social Engineering) as attackers may use such vulnerabilities to gather information about system files and directories. Regular security audits and input validation testing should be implemented to prevent similar issues in other components of the application stack, and developers should be trained on secure coding practices to avoid similar path traversal vulnerabilities in future implementations.