OpenMRS ModuleResourcesServlet has Path Traversal that Leads to Arbitrary File Read

Affected Versions

version ≤ 2.7.8 (latest version at time of disclosure)

https://github.com/openmrs/openmrs-core

Impact

The /openmrs/moduleResources/{moduleid} endpoint in OpenMRS Core is vulnerable to a path traversal attack. The ModuleResourcesServlet does not properly validate user-supplied path input, allowing an attacker to traverse directories and read arbitrary files from the server filesystem (e.g., /etc/passwd, application configuration files containing database credentials).

This endpoint serves static module resources (CSS, JS, images) and is not protected by authentication filters, as these resources are required for rendering the login page. Therefore, this vulnerability can be exploited by an unauthenticated attacker.

Note: Successful exploitation requires the target deployment to run on Apache Tomcat < 8.5.31, where the ..; path parameter bypass is not mitigated by the container. Deployments on Tomcat ≥ 8.5.31 / ≥ 9.0.10 are protected at the container level, though the underlying code defect remains.

Steps to Reproduce

1. Identify a valid installed module ID on the target OpenMRS instance (e.g., legacyui).
2. Send the following HTTP request:

3. The server responds with HTTP 200 and the contents of /etc/passwd:

Root Cause Analysis

The vulnerability exists in ModuleResourcesServlet.java (web/src/main/java/org/openmrs/module/web/ModuleResourcesServlet.java).

The getFile() method constructs a filesystem path from user-controlled input without performing path boundary validation:

protected File getFile(HttpServletRequest request) {
    // Step 1: User-controlled path input
    String path = request.getPathInfo();

    // Step 2: Extract module from path prefix
    Module module = ModuleUtil.getModuleForPath(path);
    if (module == null) { return null; }

    // Step 3: Strip module ID prefix — no traversal check
    String relativePath = ModuleUtil.getPathForResource(module, path);

    // Step 4: Concatenate into absolute path
    String realPath = getServletContext().getRealPath("")
        + MODULE_PATH
        + module.getModuleIdAsPath()
        + "/resources"
        + relativePath;  // contains "/../../../etc/passwd"

    realPath = realPath.replace("/", File.separator);

    // Step 5: No normalize().startsWith() boundary check
    File f = new File(realPath);
    if (!f.exists()) { return null; }

    return f;  // Arbitrary file returned to client
}

The helper method ModuleUtil.getPathForResource() only strips the module ID prefix and performs no sanitization:

public static String getPathForResource(Module module, String path) {
    if (path.startsWith("/")) {
        path = path.substring(1);
    }
    return path.substring(module.getModuleIdAsPath().length());
    // Returns unsanitized remainder, e.g., "/../../../../../../etc/passwd"
}

The resulting path resolves as:

{webapp}/WEB-INF/view/module/legacyui/resources/../../../../../../etc/passwd
  → /etc/passwd

Notably, the same codebase already implements correct path traversal protection in StartupFilter.java:

// StartupFilter.java — correct protection
fullFilePath = fullFilePath.resolve(httpRequest.getPathInfo());
if (!(fullFilePath.normalize().startsWith(filePath))) {
    log.warn("Detected attempted directory traversal...");
    return;  // Request rejected
}

This check is absent from ModuleResourcesServlet.

Remediation

Add a path boundary check after constructing realPath and before returning the File object. The fix should use normalize() + startsWith() to ensure the resolved path stays within the allowed module resources directory:

File f = new File(realPath);
Path allowedBase = Paths.get(getServletContext().getRealPath(""), "WEB-INF", "view", "module");
if (!f.toPath().normalize().startsWith(allowedBase.normalize())) {
    log.warn("Blocked path traversal attempt: {}", request.getPathInfo());
    return null;
}

This is consistent with the existing pattern used in StartupFilter.java and TestInstallUtil.java within the same project.