CVE-2021-32714 — hyper
CRITICALCVE-2021-32714 is a critical-severity (CVSS 9.1) CWE-190 vulnerability in hyper. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for hyper — see the affected versions and patch details below.
Integer Overflow in Chunked Transfer-Encoding
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
hyperReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Summary
hyper's HTTP server and client code had a flaw that could trigger an integer overflow when decoding chunk sizes that are too big. This allows possible data loss, or if combined with an upstream HTTP proxy that allows chunk sizes larger than hyper does, can result in "request smuggling" or "desync attacks".
Vulnerability
Example:
GET / HTTP/1.1
Host: example.com
Transfer-Encoding: chunked
f0000000000000003
abc
0
hyper only reads the rightmost 64-bit integer as the chunk size. So it reads f0000000000000003 as 3. A loss of data can occur since hyper would then read only 3 bytes of the body. Additionally, an HTTP request smuggling vulnerability would occur if using a proxy which instead has prefix truncation in the chunk size, or that understands larger than 64-bit chunk sizes.
Read more about desync attacks: https://portswigger.net/research/http-desync-attacks-request-smuggling-reborn
Impact
To determine if vulnerable to data loss, these things must be true:
- Using HTTP/1.1. Since HTTP/2 does not use chunked encoding, it is not vulnerable.
- Using hyper as a server or client. The body would be improperly truncated in either case.
- Users send requests or responses with chunk sizes greater than 18 exabytes.
To determine if vulnerable to desync attacks, these things must be true:
- Using an upstream proxy that allows chunks sizes larger than 64-bit. If the proxy rejects chunk sizes that are too large, that request won't be forwarded to hyper.
Patches
We have released the following patch versions:
- v0.14.10 (to be released when this advisory is published)
Workarounds
Besides upgrading hyper, you can take the following options:
- Reject requests manually that contain a
Transfer-Encodingheader. - Ensure any upstream proxy rejects
Transfer-Encodingchunk sizes greater than what fits in 64-bit unsigned integers.
Credits
This issue was initially reported by Mattias Grenfeldt and Asta Olofsson.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | hyper | all versions | 0.14.10cargo update -p hyper --precise 0.14.10 |
Affected Products
hyperhyperResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hyper, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hyper to 0.14.10 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32714 is resolved across your whole dependency graph.
Workarounds
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
Frequently Asked Questions
Is CVE-2021-32714 in your dependencies?
Find it across crates.io, including transitive dependencies.