hyper's HTTP server code had a flaw that incorrectly understands some requests with multiple transfer-encoding headers to have a chunked payload, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that understands the request payload boundary differently can result in "request smuggling" or "desync attacks".
The flaw was introduced in https://github.com/hyperium/hyper/commit/26417fc24a7d05df538e0f39239b373c5c3d61f6, released in v0.12.0.
Consider this example request:
POST /yolo HTTP/1.1
Transfer-Encoding: chunked
Transfer-Encoding: cow
This request should be rejected, according to RFC 7230, since it has a Transfer-Encoding
header, but after folding, it does not end in chunked
. hyper would notice the chunked
in the first line, and then check the second line, and thanks to a missing boolean assignment, not set the error condition. hyper would treat the payload as being chunked
. By differing from the spec, it is possible to send requests like these to endpoints that have different HTTP implementations, with different interpretations of the payload semantics, and cause "desync attacks".
There are several parts of the spec that must also be checked, and hyper correctly handles all of those. Additionally, hyper's client does not allow sending requests with improper headers, so the misunderstanding cannot be propagated further.
Read more about desync attacks: https://portswigger.net/research/http-desync-attacks-request-smuggling-reborn
To determine if vulnerable, all these things must be true:
transfer-encoding
.We have released and backported the following patch versions:
Besides upgrading hyper, you can take the following options:
transfer-encoding
header.transfer-encoding
correctly.This issue was initially reported by ZeddYu Lu From Qi An Xin Technology Research Institute.
{ "nvd_published_at": null, "github_reviewed_at": "2021-08-18T21:07:17Z", "severity": "MODERATE", "github_reviewed": true, "cwe_ids": [ "CWE-444" ] }