RUSTSEC-2021-0078: Lenient `hyper` header parsing of `Content-Length` could allow request smuggling

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

hyper's HTTP header parser accepted, according to RFC 7230, illegal contents inside Content-Length headers. Due to this, upstream HTTP proxies that ignore the header may still forward them along if it chooses to ignore the error.

To be vulnerable, hyper must be used as an HTTP/1 server and using an HTTP proxy upstream that ignores the header's contents but still forwards it. Due to all the factors that must line up, an attack exploiting this vulnerability is unlikely.

References

• Package: crates.io/crates/hyper
• Advisory: rustsec.org/advisories/RUSTSEC-2021-0078.html
• Web: github.com/hyperium/hyper/commit/1fb719e0b61a4f3d911562a436a2ff05fd7cb759

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 CriticalRUSTSEC-2021-0079 · 2021-07-07Integer overflow in `hyper`'s parsing of the `Transfer-Encoding` header leads to data loss
• UnsoundRUSTSEC-2022-0022 · 2022-05-10Parser creates invalid uninitialized value

Full security history of hyper