Vulnerability · Published Jun 26, 2026 · Assigned by GitHub_M
CVE-2026-48743Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length
High 7.5
In plain English
A high-severity security flaw in envoy from envoyproxy. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 23% of all known vulnerabilities).
Official description
Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, Envoy can translate a downstream HTTP/3 request that is complete at the transport layer (HEADERS with FIN / headers-only close) but still carries a nonzero Content-Length into a complete upstream HTTP/1 request with unresolved body debt. In an HTTP/1 upstream deployment where the origin replies before reading the declared body and keeps the connection reusable, the beginning of the next Envoy-generated upstream request can be consumed as the first request's body. The remaining bytes are then parsed by the origin as a new HTTP/1 request. This was reproduced as a route-bypass/desync: direct /pwn was denied by Envoy, but the second downstream H3 stream received the response for backend-parsed GET /pwn HTTP/1.1. This vulnerability is fixed in 1.35.11, 1.36.7, 1.37.3, and 1.38.1.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| envoyproxy | envoy | >= 1.38.0, < 1.38.1>= 1.37.0, < 1.37.3>= 1.36.0, < 1.36.7>= 1.35.0, < 1.35.11 |
Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N
References
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-8phg-2h2q-jgxf x_refsource_CONFIRM