In October 2022, a critical vulnerability surfaced in the Rust ecosystem—specifically in the way the conduit-hyper crate handled incoming HTTP requests. This vulnerability, registered as CVE-2022-39294, shows how oversight in handling input sizes can open the door to denial-of-service (DoS) attacks, even in modern, memory-safe languages like Rust.

In this article, we’ll break down what went wrong, demonstrate the exploit with code, explain the fix, and discuss why you probably shouldn’t put conduit-hyper directly on the frontlines of your web infrastructure.

What Is conduit-hyper?

conduit-hyper is a bridge library that connects conduit—a web application interface in Rust—to hyper, a fast HTTP implementation. It’s used as a web server layer in some Rust applications, notably in parts of crates.io (the public Rust package registry).

The Problem

Before version .4.2, conduit-hyper did not enforce any limit on how big a request’s body could be. This meant attackers could send an HTTP request with a huge Content-Length header, and conduit-hyper would try to read the entire payload into memory by calling hyper::body::to_bytes with no checks.

Why is this so dangerous?

- No Limit: Without bounds, attackers can ask the server to allocate hundreds of megabytes or even gigabytes of memory.
- Out-of-Memory: The server will try to honor the request until it runs out of memory, which could lead to a Rust panic and bring down the process (DoS).
- Low Effort, High Impact: The attacker doesn’t need many resources—just a script to send a malformed request.

Real-World Risk

While conduit-hyper is used in core Rust infrastructure, like crates.io, crates.io itself is not affected. This is because they run behind a cloud layer that filters out these massive, bogus requests before they even reach the Rust service.

However, if you were to use conduit-hyper in your public-facing application, this vulnerability could bring your server down with a single malicious request.

Exploit in Simple Terms

Suppose you run a conduit-hyper server at http://localhost:400, here’s what an attack could look like using curl and a little bash magic (don’t run this on a real target!).

# Generate a request with gigantic Content-Length
curl -X POST http://localhost:400/upload \
     -H "Content-Type: application/octet-stream" \
     -H "Content-Length: 100000000" \
     --data-binary "@<(head -c 100000000 /dev/zero)"

Here’s a simplified Rust code snippet before the fix

// This is not safe in the original pre-.4.2 conduit-hyper
use hyper::body::to_bytes;

async fn handle_request(req: Request<Body>) -> Response<Body> {
    // No size checking!
    let body_bytes = to_bytes(req.into_body()).await.unwrap();
    // Use body_bytes as needed
    Response::new(Body::from("OK"))
}

There’s no guard here: if the request is huge, the server will panic when memory runs out.

The Fix: Setting a Reasonable Limit

The fix landed in conduit-hyper .4.2, where the maximum allowed body size per request is set at 128 MiB.

Now, the code checks for size first

// Pseudocode for fixed logic (since conduit-hyper code is internal)
use hyper::Request;
use hyper::body::HttpBody;

const MAX_BODY_SIZE: usize = 134_217_728; // 128 MiB

async fn safe_handle_request(req: Request<Body>) -> Response<Body> {
    let mut size = usize;
    let mut body = req.into_body();
    while let Some(chunk) = body.data().await {
        let chunk = chunk.unwrap();
        size += chunk.len();
        if size > MAX_BODY_SIZE {
            // Reject request gracefully
            return Response::builder()
                .status(400)
                .body(Body::from("Request body too large"))
                .unwrap();
        }
    }
    // ... proceed normally ...
    Response::new(Body::from("OK"))
}

Responsible Disclosure & References

The conduit-hyper team promptly fixed the issue and released a patch. You can read the official announcements and more technical details here:

- Official CVE Record - CVE-2022-39294
- conduit-hyper changelog .4.2
- hyper::body::to_bytes documentation

Should You Use conduit-hyper?

Even with this vulnerability fixed, conduit-hyper is not recommended for direct use in public-facing servers. The maintainers themselves caution against using it for production workloads, especially without additional layers of defense (like a reverse proxy or firewall).

Conclusion

CVE-2022-39294 in conduit-hyper serves as a textbook case: trust, but verify. Even solid, memory-safe code can fail if you don’t keep attacker behavior in mind and add the right guards before trusting client input.

If you maintain a Rust webservice, always check your dependencies for updates and advisories. And if you have to accept large file uploads, make sure you’re policing those Content-Length headers!

Timeline

Published on: 10/31/2022 19:15:00 UTC
Last modified on: 07/11/2023 20:51:00 UTC