Answer in brief
CVE-2021-21299 records a High severity (CVSS 8.1) vulnerability in Multiple Transfer-Encoding headers misinterprets request payload. The current sources do not mark it as known exploited. The current feed maps hyper (crates.io). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 8.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps hyper (crates.io). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| hypercrates.io | >=0.12.0 <0.12.36 >=0.13.0-0 <0.13.10 >=0.14.0-0 <0.14.3 | 0.12.36, 0.13.10, 0.14.3 |
Published upstream
Feb 5, 2021
Evidence: source:osv:source_dates:source-dates:recordSource modified
Oct 12, 2026
Evidence: source:osv:source_dates:source-dates:recordFirst seen by HOL
Oct 12, 2026
hyper's 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".
Quoted source text, attributed separately from HOL analysis.