Description

Micronaut's HTTP client is vulnerable to HTTP Request Header Injection

Vulnerability

Micronaut's HTTP client is vulnerable to "HTTP Request Header Injection" due to not validating request headers passed to the client.

Example of vulnerable code:

@Controller("/hello")
public class HelloController {

    @Inject
    @Client("/")
    RxHttpClient client;

    @Get("/external-exploit")...
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In the above case a query value received from a user is passed as a header value to the client. Since the client doesn't validate the header value the request headers and body have the potential to be manipulated.

For example, a user that supplies the following payload, can force the client to make multiple attacker-controlled HTTP requests.

List<String> headerData = List.of(
    "Connection: Keep-Alive", // This keeps the connection open so another request can be stuffed in.
    "",
    "",
    "POST /hello/super-secret HTTP/1.1",
    "Host: 127.0.0.1",
    "Content-Length: 31",
    "",...
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Note that using @HeaderValue instead of @QueryValue is not vulnerable since Micronaut's HTTP server does validate the headers passed to the server, so the exploit can only be triggered by using user data that is not an HTTP header (query values, form data etc.).

Impact

The attacker is able to control the entirety of the HTTP body for their custom requests. As such, this vulnerability enables attackers to perform a variant of Server Side Request Forgery.

Patches

The problem has been patched in the micronaut-http-client versions 1.2.11 and 1.3.2 and above.

Workarounds

Do not pass user data directly received from HTTP request parameters as headers in the HTTP client.

References

Fix commits

https://github.com/micronaut-projects/micronaut-core/commit/9d1eff5c8df1d6cda1fe00ef046729b2a6abe7f1

https://github.com/micronaut-projects/micronaut-core/commit/6deb60b75517f80c57b42d935f07955c773b766d

https://github.com/micronaut-projects/micronaut-core/commit/bc855e439c4a5ced3d83195bb59d0679cbd95add

For more information

If you have any questions or comments about this advisory:

Open an issue in micronaut-core

Email us at [email protected]

Credit

Originally reported by @JLLeitschuh

Mitigation

Aliases

References