Server-side request forgery¶
ID: java/ssrf
Kind: path-problem
Severity: error
Precision: high
Tags:
- security
- external/cwe/cwe-918
Query suites:
- java-code-scanning.qls
- java-security-extended.qls
- java-security-and-quality.qls
Click to see the query in the CodeQL repository
Directly incorporating user input into an HTTP request without validating the input can facilitate server-side request forgery (SSRF) attacks. In these attacks, the server may be tricked into making a request and interacting with an attacker-controlled server.
Recommendation¶
To guard against SSRF attacks, you should avoid putting user-provided input directly into a request URL. Instead, maintain a list of authorized URLs on the server; then choose from that list based on the input provided. Alternatively, ensure requests constructed from user input are limited to a particular host or more restrictive URL prefix.
Example¶
The following example shows an HTTP request parameter being used directly to form a new request without validating the input, which facilitates SSRF attacks. It also shows how to remedy the problem by validating the user input against a known fixed string.
import java.net.http.HttpClient;
public class SSRF extends HttpServlet {
private static final String VALID_URI = "http://lgtm.com";
private HttpClient client = HttpClient.newHttpClient();
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
URI uri = new URI(request.getParameter("uri"));
// BAD: a request parameter is incorporated without validation into a Http request
HttpRequest r = HttpRequest.newBuilder(uri).build();
client.send(r, null);
// GOOD: the request parameter is validated against a known fixed string
if (VALID_URI.equals(request.getParameter("uri"))) {
HttpRequest r2 = HttpRequest.newBuilder(uri).build();
client.send(r2, null);
}
}
}
References¶
Common Weakness Enumeration: CWE-918.