Know every vulnerabilitybefore it knows you.
DevGuard continuously monitors your dependencies and alerts you when CVEs like this one affect your stack — with real-time threat intelligence built for developers.
GHSA-f3pg-qwvg-p99c
No affected components available
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-Lengthheader, 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-Lengthheader. - Ensure any upstream proxy handles
Content-Lengthheaders with a plus sign prefix.
Credits
This issue was initially reported by Mattias Grenfeldt and Asta Olofsson.
The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
Browse More
Continuously monitor your dependencies and get alerted when vulnerabilities like this one affect your stack.
Checkout DevGuard