CVE-2017-20284 in Resin
Summary
by MITRE • 09/18/2026
Caucho Resin contains a path traversal vulnerability in the documentation webapp (resin-doc) that allows remote unauthenticated attackers to read arbitrary files by supplying a relative path through the inputFile request parameter of the jndi-appconfig tutorial servlet. Attackers can craft requests with directory traversal sequences to the servlet endpoint to read files outside the intended tutorial directory on the underlying system. Exploitation evidence was first observed by the Shadowserver Foundation on 2021-12-10.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified in Caucho Resin affects its documentation web application, specifically known as resin-doc. This component is intended for administrative and educational purposes but contains a critical path traversal flaw that exposes sensitive system files to remote unauthenticated attackers. The root cause lies within the jndi-appconfig tutorial servlet, which processes user-supplied input through the inputFile request parameter without adequate validation or sanitization of directory traversal sequences such as dot-dot-slash characters. This lack of proper input handling allows an attacker to manipulate the file path resolution logic, effectively breaking out of the intended sandboxed tutorial directory and accessing arbitrary files on the underlying operating system.
From a technical perspective, this flaw represents a classic insecure direct object reference combined with path traversal issues. When the servlet receives a request containing relative paths designed to escape the current working directory, it fails to normalize or restrict these inputs before passing them to file I/O operations. Consequently, an attacker can craft HTTP requests that traverse up through parent directories and then navigate down into sensitive areas of the server's filesystem. This mechanism bypasses standard access controls because the vulnerability exists at the application logic layer rather than relying on network-level permissions alone. The ability to read arbitrary files means that attackers can potentially extract configuration files, source code containing hardcoded credentials, database connection strings, or other confidential data stored in accessible locations on the disk.
The operational impact of this vulnerability is severe due to its unauthenticated nature and remote exploitability. Since no authentication is required to trigger the flaw, any entity with network access to the Resin server can attempt exploitation. The initial evidence of active exploitation was observed by the Shadowserver Foundation on December 10, 2021, indicating that this vulnerability has been actively targeted in the wild. Successful exploitation leads to a complete compromise of confidentiality for files accessible by the user account running the Resin process. This information disclosure can serve as a stepping stone for further attacks, such as privilege escalation or lateral movement within an internal network if sensitive configuration details are obtained.
In terms of industry standards classification, this vulnerability aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory and CWE-918: Server-Side Request Forgery (SSRF) implications where the server is tricked into accessing internal resources. It also maps to MITRE ATT&CK technique T1083: File and Directory Discovery, as attackers use this flaw to enumerate and access files on the target system. The lack of authentication requirement places it in a high-risk category for internet-facing services that may inadvertently expose administrative interfaces or documentation ports.
Mitigation strategies should focus primarily on disabling or removing the resin-doc web application if it is not strictly necessary for production operations, as this eliminates the attack surface entirely. If retention of the documentation interface is required, administrators must implement strict input validation to ensure that only expected file names are processed and that path traversal sequences are rejected at the servlet level. Additionally, deploying a Web Application Firewall with rules specifically targeting directory traversal patterns can provide an additional layer of defense. Regular security audits and patching of Caucho Resin to versions where this issue has been addressed by the vendor are essential steps to ensure long-term resilience against such exploitation attempts.