RUSTSEC-2021-0079: Integer overflow in `hyper`'s parsing of the `Transfer-Encoding` header leads to data loss

What to do

1. See which version you have: cargo tree -i hyper (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p hyper. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example hyper = "0.14.10") or update the dependency that pulls it in.
3. Check again with cargo audit, or paste your Cargo.lock into our Cargo.toml checker.

Details from the advisory

When decoding chunk sizes that are too large, hyper's code would encounter an integer overflow. Depending on the situation, this could lead to data loss from an incorrect total size, or in rarer cases, a request smuggling attack.

To be vulnerable, you must be using hyper for any HTTP/1 purpose, including as a client or server, and consumers must send requests or responses that specify a chunk size greater than 18 exabytes. For a possible request smuggling attack to be possible, any upstream proxies must accept a chunk size greater than 64 bits.

References

• Package: crates.io/crates/hyper
• Advisory: rustsec.org/advisories/RUSTSEC-2021-0079.html
• Web: github.com/hyperium/hyper/commit/efd9a9821fd2f1ae04b545094de76a435b62e70f

From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.

Other advisories for hyper

• Vulnerability MediumRUSTSEC-2016-0002 · 2016-05-09HTTPS MitM vulnerability due to lack of hostname verification
• Vulnerability MediumRUSTSEC-2017-0002 · 2017-01-23headers containing newline characters can split messages
• Vulnerability CriticalRUSTSEC-2020-0008 · 2020-03-19Flaw in hyper allows request smuggling by sending a body in GET requests
• Vulnerability HighRUSTSEC-2021-0020 · 2021-02-05Multiple Transfer-Encoding headers misinterprets request payload
• Vulnerability MediumRUSTSEC-2021-0078 · 2021-07-07Lenient `hyper` header parsing of `Content-Length` could allow request smuggling
• UnsoundRUSTSEC-2022-0022 · 2022-05-10Parser creates invalid uninitialized value

Full security history of hyper