CVE-2017-16135 in serverzyy
Summary
by MITRE
serverzyy is a static file server. serverzyy 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-2017-16135 affects serverzyy, a static file server implementation that suffers from a critical directory traversal flaw. This issue stems from inadequate input validation within the URL parsing mechanism, allowing remote attackers to access arbitrary files on the server filesystem through maliciously crafted requests. The vulnerability manifests when users include directory traversal sequences such as "../" in the URL path, which enables them to navigate beyond the intended document root directory and potentially access sensitive system files, configuration data, or other restricted resources.
This directory traversal vulnerability represents a classic security weakness that aligns with CWE-22, which specifically addresses improper limitation of a pathname to a restricted directory. The flaw operates by bypassing normal file access controls through the manipulation of relative path references in HTTP requests. When the server processes these malformed paths, it fails to properly sanitize or validate the input, allowing the traversal sequences to be interpreted literally rather than being neutralized or rejected. The vulnerability can be exploited by attackers who craft URLs containing multiple directory traversal components, potentially enabling them to access files outside the designated web root directory.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can provide attackers with unauthorized access to sensitive system resources including configuration files, database files, log files, and potentially even system binaries. This access could enable further exploitation attempts such as privilege escalation, data exfiltration, or system compromise. The vulnerability affects any system running serverzyy where the static file server is accessible to untrusted users, making it particularly dangerous in production environments where such servers may be exposed to the internet. The remote nature of the attack means that exploitation does not require local system access or authentication credentials, making it an attractive target for automated scanning and exploitation tools.
Mitigation strategies for CVE-2017-16135 should focus on implementing proper input validation and sanitization of all URL parameters and path components. The most effective approach involves implementing strict path validation that rejects or removes directory traversal sequences before processing file requests. This can be achieved through the implementation of white-listing mechanisms that only allow specific, safe characters and path components, or through the use of robust path normalization functions that resolve relative paths to absolute paths within the designated document root. Organizations should also consider implementing web application firewalls that can detect and block malicious path traversal attempts, as well as conducting regular security assessments to identify similar vulnerabilities in other components of their infrastructure. The remediation process should include updating to the latest version of serverzyy that addresses this vulnerability, as well as implementing comprehensive logging and monitoring to detect potential exploitation attempts. Additionally, following the principle of least privilege and implementing proper access controls can help limit the potential damage from successful exploitation attempts.
The vulnerability demonstrates how simple input validation flaws can result in severe security implications, particularly in web applications that handle file system operations. It aligns with several ATT&CK techniques including T1083 (File and Directory Discovery) and T1566 (Phishing with Malicious Attachments) where attackers might use such vulnerabilities to gain access to sensitive files and potentially escalate their attacks. Organizations should treat this vulnerability as part of a broader security posture assessment, ensuring that similar path traversal issues are not present in other applications or services within their environment. The incident underscores the importance of implementing defense-in-depth strategies and continuous security monitoring to detect and respond to exploitation attempts. Regular security training for development teams about secure coding practices, particularly regarding input validation and path handling, can help prevent similar vulnerabilities from being introduced in future software implementations.