CVE-2021-21299 Multiple Transfer-Encoding headers misinterprets request payload

What is CVE-2021-21299?

CVE-2021-21299 is a medium-severity vulnerability in hyperium hyper, published on 11 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

hyper is an open-source HTTP library for Rust (crates.io). In hyper from version 0.12.0 and before versions 0.13.10 and 0.14.3 there is a vulnerability that can enable a request smuggling attack. The 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". To determine if vulnerable, all these things must be true: 1) Using hyper as an HTTP server (the client is not affected), 2) Using HTTP/1.1 (HTTP/2 does not use transfer-encoding), 3) Using a vulnerable HTTP proxy upstream to hyper. If an upstream proxy correctly rejects the illegal transfer-encoding headers, the desync attack cannot succeed. If there is no proxy upstream of hyper, hyper cannot start the desync attack, as the client will repair the headers before forwarding. This is fixed in versions 0.14.3 and 0.13.10. As a workaround one can take the following options: 1) Reject requests that contain a `transfer-encoding` header, 2) Ensure any upstream proxy handles `transfer-encoding` correctly.

Weakness: CWE-444

Which versions are affected by CVE-2021-21299?

7 open source packages ship an affected version, including hyper. It affects 1 product.

Products include Hyper Hyper.

How do I fix CVE-2021-21299?

Upgrade hyper to a fixed version for your release line: 0.12.36, 0.13.10 or 0.14.3.

Is CVE-2021-21299 being exploited?

There is no known exploitation of CVE-2021-21299 in the wild and no public exploit code.

Other vulnerabilities in hyperium hyper

• CVE-2020-35863 HTTP Request Smuggling in hyper Critical 9.8
• CVE-2022-31394 Denial of service in n/a High 7.5
• CVE-2021-32714 Integer Overflow in Chunked Transfer-Encoding Medium 5.9
• CVE-2017-18587 Headers containing newline characters can split messages in hyper Medium 5.3
• CVE-2016-10932 HTTPS MitM vulnerability due to lack of hostname verification Medium 4.8

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CVE-2021-26959, DEBIAN-CVE-2021-21299, GHSA-6hfq-h8hq-87mf, RUSTSEC-2021-0020, UBUNTU-CVE-2021-21299, openSUSE-SU-2024:12238-1 and 2 more.