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CVE-2026-48743

Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length PUBLISHED

Description (CNA)

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 (CNA)

Vendor / productVersions
envoyproxy / envoyaffected >= 1.38.0, < 1.38.1; affected >= 1.37.0, < 1.37.3; affected >= 1.36.0, < 1.36.7; affected >= 1.35.0, < 1.35.11

CWE

CWE-444

References

ADP enrichment

CISA-ADP

No English description supplied.