Possible request smuggling in HTTP/2 due missing validation
If a Content-Length header is present in the original HTTP/2 request, the field is not validated by
Http2MultiplexHandler as it is propagated up. This is fine as long as the request is not proxied through as HTTP/1.1.
If the request comes in as an HTTP/2 stream, gets converted into the HTTP/1.1 domain objects (
HttpContent, etc.) via
Http2StreamFrameToHttpObjectCodec and then sent up to the child channel's pipeline and proxied through a remote peer as HTTP/1.1 this may result in request smuggling.
In a proxy case, users may assume the content-length is validated somehow, which is not the case. If the request is forwarded to a backend channel that is a HTTP/1.1 connection, the Content-Length now has meaning and needs to be checked.
An attacker can smuggle requests inside the body as it gets downgraded from HTTP/2 to HTTP/1.1. A sample attack request looks like:
POST / HTTP/2 :authority:: externaldomain.com Content-Length: 4 asdfGET /evilRedirect HTTP/1.1 Host: internaldomain.com
Users are only affected if all of this is
Http2StreamFrameToHttpObjectCodecis used to convert to HTTP/1.1 objects
- These HTTP/1.1 objects are forwarded to another remote peer.
This has been patched in 4.1.60.Final
The user can do the validation by themselves by implementing a custom
ChannelInboundHandler that is put in the
Related change to workaround the problem: Netflix/zuul#980