CVE-2021-21299
No exploitation reported by the sources we read.
- Published2021-02-11
- Fixed in0.14.3 · 0.13.10 · 0.12.36
- WeaknessCWE-444
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « affected ».With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.
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.
Timeline
dates in UTC- 2021-02-1118:15CVE publishedNVD
Observed activity
isMalicious corpus · updated 2026-10-23 21:37 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-21299?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-21299?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
NVD · OSV| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 0.14 | ≥ 0.14.0, < 0.14.3 | 0.14.3 | NVD · OSV |
| 0.14 | ≥ 0.14.0-0, < 0.14.3 | 0.14.3 | OSV |
| 0.x | ≥ 0.12.0, < 0.13.10 | 0.13.10 | NVD |
| 0.13 | ≥ 0.13.0-0, < 0.13.10 | 0.13.10 | OSV |
| 0.13 | ≥ 0.13.0, < 0.13.10 | 0.13.10 | OSV |
| 0.12 | ≥ 0.12.0, < 0.12.36 | 0.12.36 | OSV |
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Fix
- Update Hyper to 0.14.3 · 0.13.10 · 0.12.36
Advisories and patches
- github.comPatch
Detection
- Nuclei template
- none so far ProjectDiscovery
- Exploit-DB
- no entry Exploit-DB
- Proof-of-concept repositories
- none listed PoC-in-GitHub
Sources
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- Published
- 2021-02-11
- Last Modified
- 2026-06-17
- NVD status
- Modified
Frequently asked questions
What is CVE-2021-21299?
Is CVE-2021-21299 actively exploited?
What is the CVSS score for CVE-2021-21299?
Running hyper? Hear about its next vulnerability
Surveillance reads the versions in your stack — a domain, a lockfile or a list — checks each CVE against the ranges its sources publish, and alerts you when one you run is exploited or enters CISA KEV. A version it cannot read stays « version not verified ».
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