Source: cve@mitre.org
Vulnerabilities in UMN gopher and gopher+ versions 1.12 and 2.0x allow an intruder to read any files that can be accessed by the gopher daemon.
Gopher servers running vulnerable versions are susceptible to a critical vulnerability allowing attackers to read arbitrary files accessible to the gopher daemon. This can lead to sensitive data exposure, including configuration files, user credentials, and potentially the compromise of the entire system. Immediate patching or mitigation is crucial to prevent exploitation.
Step 1: Target Identification: The attacker identifies a gopher server running a vulnerable version (1.12 or 2.0x).
Step 2: Crafting the Malicious Request: The attacker crafts a gopher request that includes a specially crafted file path. This path uses techniques like ../ to traverse the directory structure and request files outside the intended scope.
Step 3: Request Submission: The attacker sends the malicious gopher request to the vulnerable server.
Step 4: Server Processing: The gopher server receives the request and, due to the lack of input validation, constructs a file path based on the attacker's input.
Step 5: File Retrieval: The server attempts to retrieve the file specified by the crafted path. Because the gopher daemon has access to these files, the server successfully retrieves the contents.
Step 6: Data Exfiltration: The server sends the contents of the requested file back to the attacker, allowing them to access sensitive information.
Root Cause: The vulnerability stems from insufficient input validation and access control within the UMN gopher and gopher+ server implementations. Specifically, the server fails to properly sanitize user-supplied input used to construct file paths for retrieval. This allows an attacker to craft malicious gopher requests that specify arbitrary file paths, bypassing intended access restrictions. The server then retrieves and serves the contents of these files, effectively granting unauthorized access. The lack of proper boundary checks and access control mechanisms allows for path traversal attacks, enabling attackers to read any file the gopher daemon has permissions to access.
This vulnerability is not directly associated with specific APT groups or malware campaigns in recent years due to its age and the obsolescence of the affected software. However, it's a good example of a vulnerability that could be exploited by any attacker with basic skills. It is not listed in CISA KEV.
Monitor gopher server logs for suspicious file access attempts, especially those involving path traversal characters (e.g., ../).
Analyze network traffic for unusual gopher requests, particularly those requesting sensitive files (e.g., /etc/passwd, /etc/shadow, configuration files).
Use file integrity monitoring (FIM) tools to detect unauthorized modifications to critical system files.
Implement intrusion detection systems (IDS) with signatures specifically designed to detect gopher path traversal attempts.
Patching: The primary remediation is to upgrade to a non-vulnerable version of the gopher server software. Since the software is old, this may not be possible. Consider removing the gopher server if it is not needed.
Input Validation: Implement robust input validation to sanitize all user-supplied input used in file path construction. This should include filtering out path traversal characters and limiting the scope of accessible files.
Access Control: Restrict the gopher daemon's access to only the necessary files and directories. Employ the principle of least privilege.
Network Segmentation: Isolate the gopher server within a separate network segment to limit the impact of a successful exploit.
Disable Gopher: If the gopher service is not essential, disable it to eliminate the attack surface.