Summary
hyper's HTTP/1 server code had a flaw that incorrectly parses and accepts requests with a Content-Length header with a prefixed plus sign, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that doesn't parse such Content-Length headers, but forwards them, can result in "request smuggling" or "desync attacks".
Vulnerability
The flaw exists in all prior versions of hyper, if built with rustc v1.5.0 or newer.
Example:
GET / HTTP/1.1
Host: example.com
Content-Length: +3
abc
This request gets accepted and hyper reads the body as abc. The request should be rejected, according to RFC 7230, since the ABNF for Content-Length only allows for DIGITs. This is due to using the FromStr implementation for u64 in the standard library. 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".
In this particular case, an upstream proxy would need to error when parsing the Content-Length, but not reject the request (swallowing its own error), and forwarding the request as-is with the Content-Length still included. Then the upstream proxy and hyper would disagree on the length of the request body. The combination of these factors would be extremely rare.
Read more about desync attacks: https://portswigger.net/research/http-desync-attacks-request-smuggling-reborn
Impact
To determine if vulnerable, all these things must be true:
- Using hyper as an HTTP server. While the lenient decoder also exists in the client, a vulnerability does not exist around responses.
- Using HTTP/1. The HTTP/2 code uses a stricter parser.
- Using a vulnerable HTTP proxy upstream to hyper. If an upstream proxy correctly rejects the illegal
Content-Length header, OR can parse the length with the plus sign, the desync attack cannot succeed.
Patches
We have released the following patch versions:
- v0.14.10 (to be released when this advisor is published)
Workarounds
Besides upgrading hyper, you can take the following options:
- Reject requests manually that contain a plus sign prefix in the
Content-Length header.
- Ensure any upstream proxy handles
Content-Length headers with a plus sign prefix.
Credits
This issue was initially reported by Mattias Grenfeldt and Asta Olofsson.
mattiasgrenfeldt Analyst
asta12 Analyst
Summary
hyper's HTTP/1 server code had a flaw that incorrectly parses and accepts requests with a
Content-Lengthheader with a prefixed plus sign, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that doesn't parse suchContent-Lengthheaders, but forwards them, can result in "request smuggling" or "desync attacks".Vulnerability
The flaw exists in all prior versions of hyper, if built with
rustcv1.5.0 or newer.Example:
This request gets accepted and hyper reads the body as abc. The request should be rejected, according to RFC 7230, since the ABNF for
Content-Lengthonly allows forDIGITs. This is due to using theFromStrimplementation foru64in the standard library. 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".In this particular case, an upstream proxy would need to error when parsing the
Content-Length, but not reject the request (swallowing its own error), and forwarding the request as-is with theContent-Lengthstill included. Then the upstream proxy and hyper would disagree on the length of the request body. The combination of these factors would be extremely rare.Read more about desync attacks: https://portswigger.net/research/http-desync-attacks-request-smuggling-reborn
Impact
To determine if vulnerable, all these things must be true:
Content-Lengthheader, OR can parse the length with the plus sign, the desync attack cannot succeed.Patches
We have released the following patch versions:
Workarounds
Besides upgrading hyper, you can take the following options:
Content-Lengthheader.Content-Lengthheaders with a plus sign prefix.Credits
This issue was initially reported by Mattias Grenfeldt and Asta Olofsson.