CVE-2017-16090 in fsk-server
Summary
by MITRE
fsk-server is a simple http server. fsk-server 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 • 02/15/2020
The fsk-server directory traversal vulnerability represents a critical security flaw that enables unauthorized access to underlying filesystem resources through manipulated url parameters. This vulnerability specifically affects the fsk-server http server implementation, which processes user requests without proper input validation or sanitization mechanisms. The flaw manifests when an attacker crafts malicious urls containing directory traversal sequences such as "../" which allows them to navigate beyond the intended web root directory and access files that should remain restricted. This type of vulnerability falls under the common weakness enumeration CWE-22, which classifies directory traversal attacks as a fundamental security issue where applications fail to properly validate user-supplied input that contains path traversal sequences.
The technical implementation of this vulnerability stems from inadequate input filtering within the server's request handling logic. When the fsk-server processes incoming http requests, it fails to sanitize url parameters that contain relative path references, allowing attackers to manipulate the file system navigation paths. The server essentially treats user input as trusted content without validating or normalizing the path components, creating an opportunity for malicious actors to access sensitive files, configuration data, or system resources that reside outside the designated web serving directory. This vulnerability can be exploited through simple http GET requests where the attacker appends directory traversal sequences to standard file paths, potentially accessing system files, application source code, database files, or other confidential information stored on the server.
The operational impact of this directory traversal vulnerability extends beyond simple information disclosure, as it can lead to complete system compromise depending on the server configuration and file permissions. An attacker with access to the filesystem through this vulnerability can potentially read sensitive configuration files that may contain database credentials, API keys, or other authentication tokens. The vulnerability also opens pathways for further exploitation including arbitrary code execution if the server has write permissions to critical directories, or privilege escalation if the server process runs with elevated system privileges. This type of attack vector aligns with several techniques documented in the attack tactic framework, particularly those related to privilege escalation and information gathering phases of the attack lifecycle.
Mitigation strategies for this vulnerability require implementing proper input validation and sanitization mechanisms within the fsk-server application. The most effective approach involves normalizing all user-supplied path parameters by removing or encoding directory traversal sequences before processing file requests. Implementing a whitelist-based approach that only allows specific, safe file paths can prevent unauthorized access attempts. Additionally, the server should operate with minimal required privileges and implement proper file system access controls to limit what files can be accessed even if traversal attempts are successful. Security configurations should include disabling directory listing features and implementing proper authentication mechanisms to reduce the attack surface. Organizations should also consider deploying web application firewalls and intrusion detection systems that can identify and block suspicious path traversal patterns in real-time. Regular security assessments and code reviews focusing on input validation practices can help identify similar vulnerabilities in other applications and prevent future incidents.