CVE-2017-16195 in pytservce
Summary
by MITRE
pytservce is a static file server. pytservce is vulnerable to a directory traversal issue, giving an attacker access to the filesystem by placing "../" in the url.
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Analysis
by VulDB Data Team • 02/16/2020
The vulnerability identified as CVE-2017-16195 affects pytservce, a static file server implementation that serves files directly from the filesystem without proper input validation. This directory traversal flaw represents a critical security weakness that allows remote attackers to access arbitrary files on the server's filesystem by manipulating URL parameters. The vulnerability stems from the server's failure to sanitize or validate file paths before processing user-supplied input, creating an opportunity for malicious actors to navigate beyond the intended directory structure.
The technical implementation of this vulnerability occurs when the pytservce application processes URLs containing directory traversal sequences such as "../" which are commonly used to move up directory levels in file systems. When these sequences are present in the URL path, the server fails to properly validate or sanitize the input, allowing the attacker to bypass normal access controls and retrieve files from locations outside the designated web root directory. This type of vulnerability is classified as a path traversal attack and maps directly to CWE-22, which describes improper limitation of a pathname to a restricted directory. The flaw is particularly dangerous because it can potentially expose sensitive files including configuration data, source code, system credentials, or other confidential information stored on the server.
The operational impact of CVE-2017-16195 extends beyond simple information disclosure, as it can enable attackers to gain unauthorized access to the underlying operating system. An attacker could potentially access system files, user data, application configuration files, or even execute arbitrary commands if the server is running with elevated privileges. The vulnerability is particularly concerning in environments where pytservce is used to serve content in production or development scenarios, as it could compromise entire server infrastructures. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1083, which covers discovering file and directory permissions, and T1566, which involves the initial access phase of attack chains. The ease of exploitation makes this vulnerability particularly dangerous as it requires minimal technical skill to leverage.
Mitigation strategies for this vulnerability must address the fundamental flaw in input validation and path handling within the pytservce application. The most effective approach involves implementing proper input sanitization and validation mechanisms that reject or normalize directory traversal sequences before processing file paths. Organizations should immediately update to patched versions of pytservce if available, or implement web application firewalls that can detect and block suspicious path traversal patterns in incoming requests. Additional protective measures include restricting file server access to trusted networks, implementing proper access controls and authentication mechanisms, and conducting regular security audits of file serving applications. The vulnerability highlights the importance of following secure coding practices and input validation principles as outlined in OWASP Top Ten and other security standards, emphasizing that all user-supplied data must be treated as potentially malicious until properly validated and sanitized.