CVE-2026-48743

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

HIGH

7.5

CVSS Score

Published: June 26, 2026 at 05:34 PM UTC

Updated: October 25, 2026 at 05:10 PM UTC

1 product affected across 1 vendorEnvoy

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Severity

HIGH7.5

Exploit prediction

EPSS 0.3%

SSVC

PoC

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Envoy · Envoyproxy

95%

1.35.0 ≤ v < 1.35.131.36.0 ≤ v < 1.36.91.37.0 ≤ v < 1.37.51.38.0 ≤ v < 1.38.3

Affected range stops below 1.35.11, so it looks safe — our inference, not a vendor statement

Affected range stops below 1.35.13, so it looks safe — our inference, not a vendor statement

Affected range stops below 1.36.7, so it looks safe — our inference, not a vendor statement

Affected range stops below 1.36.9, so it looks safe — our inference, not a vendor statement

Affected range stops below 1.37.3, so it looks safe — our inference, not a vendor statement

Affected range stops below 1.37.5, so it looks safe — our inference, not a vendor statement

Affected range stops below 1.38.1, so it looks safe — our inference, not a vendor statement

Affected range stops below 1.38.3, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://github.com/envoyproxy/envoy/security/advisories/GHSA-8phg-2h2q-jgxf

References (1)

x_refsource_CONFIRMExploitVendor AdvisoryMitigation

Source: cverecord

https://github.com/envoyproxy/envoy/security/advisories/GHSA-8phg-2h2q-jgxf

SSVC — Action Prioritization

SSVCPoCNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.5HIGHGitHub_M

Attack Vector: NETWORK
Complexity: HIGH
Privileges: NONE
User Interaction: NONE
Scope: CHANGED
Confidentiality: LOW
Integrity: HIGH
Availability: NONE

Vector?

Quick Info

StatusANALYZED

CWE

CWE-444

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