CVE-2017-16171 in hcbserver
Summary
by MITRE
hcbserver is a static file server. hcbserver 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 hcbserver static file server vulnerability represents a critical directory traversal flaw that exposes systems to unauthorized file system access. This vulnerability stems from inadequate input validation within the web server's path handling mechanism, allowing malicious actors to manipulate URL parameters to navigate beyond the intended document root directory. The flaw specifically manifests when the server fails to properly sanitize user-supplied paths containing relative path traversal sequences such as "../" which should be rejected or properly resolved to prevent access to parent directories. The vulnerability is classified under CWE-22 as Improper Limitation of a Pathname to a Restricted Directory, a well-known weakness in web application security that has been consistently exploited across various platforms and servers.
The technical exploitation of this vulnerability occurs when an attacker crafts malicious URLs that include directory traversal sequences, enabling them to access files and directories that should remain restricted. When hcbserver processes these crafted requests, it fails to properly validate or normalize the requested paths, allowing the traversal to occur. This can result in access to sensitive system files, configuration data, application source code, or other confidential information stored outside the web server's intended document root. The impact is particularly severe because static file servers typically serve content from predictable locations, making it easier for attackers to map the underlying file system structure and identify valuable targets. The vulnerability operates at the application layer and can be exploited through simple HTTP requests without requiring authentication or special privileges, making it highly dangerous in environments where the server is accessible to untrusted users.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can lead to complete system compromise when combined with other attack vectors. An attacker who successfully exploits this vulnerability can potentially access database files, application configuration files containing database credentials, system logs, or even system binaries that could provide further attack surface. The vulnerability also enables attackers to execute arbitrary code if they can place malicious files in accessible directories, or to read system files that may contain sensitive information such as password hashes or private keys. This type of vulnerability aligns with ATT&CK technique T1083 which covers File and Directory Discovery, and T1566 which covers Phishing with Malicious Attachments, as attackers often use directory traversal to gather intelligence about target systems. The exposure of the file system through directory traversal can also facilitate privilege escalation attacks, where attackers use the access to system files to gain higher privileges or to pivot to other systems within the network.
Mitigation strategies for this vulnerability involve implementing proper input validation and path sanitization mechanisms within the web server software. Organizations should ensure that all user-supplied paths are properly validated and normalized before being processed, rejecting any requests containing directory traversal sequences or resolving paths to prevent access outside the intended directory structure. The recommended approach includes implementing a whitelist-based validation system that only allows specific, safe characters and paths while rejecting potentially dangerous sequences such as "../", "..\", or similar patterns. Additionally, deploying web application firewalls and implementing proper access controls can provide additional layers of protection against such attacks. Regular security audits and code reviews should specifically focus on input validation mechanisms and path handling to prevent similar vulnerabilities from being introduced in future versions of the software. The vulnerability also highlights the importance of following secure coding practices as outlined in OWASP Top Ten and the ISO/IEC 27001 security standards, particularly in the areas of input validation and access control.