CVE-2017-16762 in Sanic
Summary
by MITRE
Sanic before 0.5.1 allows reading arbitrary files with directory traversal, as demonstrated by the /static/..%2f substring.
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-16762 represents a critical directory traversal flaw in the Sanic web framework version 0.5.0 and earlier. This security weakness enables malicious actors to access arbitrary files on the server by exploiting improper input validation in the static file serving functionality. The vulnerability manifests when the application processes requests containing directory traversal sequences such as the demonstrated /static/..%2f substring, which allows attackers to navigate outside the intended static file directory and access sensitive system files. The flaw stems from insufficient sanitization of user-supplied paths, particularly in the route handling mechanism that processes static file requests. This issue directly maps to CWE-22, which categorizes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. The vulnerability affects applications that rely on Sanic's built-in static file serving capabilities without proper input validation or additional security measures.
The technical implementation of this vulnerability exploits the framework's default behavior of serving static files without adequate path normalization or validation. When a request is made with a path containing directory traversal sequences like ..%2f, the Sanic framework fails to properly sanitize or resolve these paths, allowing the underlying file system to interpret the traversal components and return files from unintended locations. This flaw operates at the application layer and can be exploited through simple HTTP requests without requiring authentication or special privileges. The impact extends beyond mere file access to potentially include sensitive information disclosure, as attackers can retrieve configuration files, source code, database credentials, or other confidential data stored on the server. The vulnerability demonstrates a fundamental flaw in input validation and path resolution within the web framework's static file handling mechanism, making it particularly dangerous for applications that serve static content without additional security controls.
The operational impact of CVE-2017-16762 can be severe and far-reaching for affected organizations. Attackers can leverage this vulnerability to compromise entire server environments by accessing critical system files, application configuration data, and potentially database connection strings or API keys. The vulnerability aligns with ATT&CK technique T1213.002, which involves data from information repositories, as it enables unauthorized access to stored application data and configuration files. Organizations running vulnerable Sanic applications face risks including data breaches, regulatory compliance violations, and potential system compromise. The attack surface is particularly broad since many web applications use static file serving for serving CSS, JavaScript, images, and other resources, making this vulnerability applicable to a wide range of deployed systems. The exploitation is straightforward and requires minimal technical expertise, making it a popular target for automated attacks and malicious actors seeking to gain unauthorized access to server resources.
Mitigation strategies for CVE-2017-16762 primarily focus on upgrading to Sanic version 0.5.1 or later, where the directory traversal vulnerability has been addressed through improved input validation and path sanitization. Organizations should implement comprehensive input validation at multiple layers, including application-level sanitization of file paths and proper path normalization before file access operations. Network-level controls such as web application firewalls can provide additional protection by filtering out suspicious path traversal sequences and monitoring for known attack patterns. Security practitioners should also consider implementing principle of least privilege for static file directories, ensuring that static file serving paths are restricted to only necessary directories and that file permissions are properly configured. The vulnerability highlights the importance of following secure coding practices and input validation as outlined in OWASP Top Ten and other security frameworks. Regular security testing and vulnerability assessments should include checks for similar path traversal vulnerabilities in other components of the application stack, as this type of flaw is common across many web frameworks and applications. Organizations should also implement proper monitoring and logging of file access patterns to detect potential exploitation attempts.