What is the CVSS score of CVE-2026-48743?

CVE-2026-48743 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N. EPSS exploitation probability: 0.3%.

Which versions of Envoy are affected by CVE-2026-48743?

Envoy proxy versions prior to specified patch releases contain an HTTP request smuggling vulnerability (CVE-2026-48743) that allows remote attackers to desynchronize upstream connections and route…. A patch is available.

How to fix or mitigate CVE-2026-48743?

Within 24 hours: Catalog all Envoy proxy deployments and document current versions. Within 7 days: Identify instances running versions prior to 1.35.11 (1.35 track), 1.36.7 (1.36 track), 1.37.3 (1.37 track), or 1.38.1 (1.38 track). Within 30 days: Implement compensating controls including HTTP/1 connection reuse limits, strict Content-Length and Transfer-Encoding validation, and smuggling-pattern detection rules.

Envoy CVE-2026-48743

EUVD-2026-39822 HIGH

HTTP Request/Response Smuggling (CWE-444)

2026-06-26 GitHub_M

Request Smuggling Authentication Bypass Envoy Red Hat Suse

7.5

CVSS 3.1 · Vendor: GitHub_M

Severity by source

Vendor (GitHub_M) PRIMARY

7.5 HIGH

AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N

vuln.today AI

7.5 HIGH

Network-reachable and unauthenticated (AV:N/PR:N); AC:H for the upstream early-response/connection-reuse race; scope change (S:C) as a separate backend connection is desynced; I:H for request injection/route bypass, C:L, A:N.

3.1 AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N

4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:H/VA:N/SC:L/SI:H/SA:N

SUSE

HIGH

qualitative

Red Hat

7.5 HIGH

qualitative

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

Low

Integrity

High

Availability

None

Lifecycle Timeline

Patch available

Jun 26, 2026 - 19:02 EUVD

Analysis Generated

Jun 26, 2026 - 18:32 vuln.today

DescriptionCVE.org

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.

AnalysisAI

HTTP request smuggling in Envoy proxy (versions prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1) lets remote attackers desynchronize HTTP/1 upstream connections by sending an HTTP/3 downstream request that is transport-complete (HEADERS with FIN) yet declares a nonzero Content-Length, leaving the translated HTTP/1 request with unresolved body debt. When the HTTP/1 origin replies before reading the body and keeps the connection reusable, the start of Envoy's next upstream request is consumed as the prior request's body, and the remainder is parsed by the origin as a separate, attacker-controlled request. This was demonstrated as a route-bypass: a directly denied /pwn was served to a second downstream stream as a backend-parsed GET /pwn, with no public exploit identified at time of analysis and no CISA KEV listing.

Technical ContextAI

Envoy is a widely used cloud-native edge and service proxy that terminates downstream protocols (here HTTP/3) and re-encodes requests to upstream origins (here HTTP/1.1). The flaw is a protocol-translation defect: an HTTP/3 stream can be complete at the transport layer (headers-only close via FIN) while still advertising a nonzero Content-Length, and Envoy translated this into an HTTP/1 request whose declared body was never satisfied ('body debt'). This is a classic CWE-444 HTTP Request/Response Smuggling (desync) condition arising from inconsistent message-framing interpretation between the HTTP/3 front end and the HTTP/1 back end. Per the CPE cpe:2.3:a:envoyproxy:envoy, the affected component is the Envoy data plane itself, and exploitation depends on the upstream HTTP/1 origin's behavior of responding before fully draining the request body while reusing the connection.

RemediationAI

Upgrade to the patched release for your branch: Vendor-released patch versions are 1.35.11, 1.36.7, 1.37.3, or 1.38.1 (apply the one matching your current minor line) as documented in GHSA-8phg-2h2q-jgxf (https://github.com/envoyproxy/envoy/security/advisories/GHSA-8phg-2h2q-jgxf). If immediate patching is not possible, reduce exposure by avoiding HTTP/1.1 upstream connections where feasible - configure upstreams to HTTP/2 (which is not subject to this HTTP/1 body-debt desync), at the cost of requiring HTTP/2-capable origins. As a further compensating control, disable upstream HTTP/1 connection reuse/keep-alive (set max requests per upstream connection to 1) so smuggled bytes cannot bleed into a reused connection; this carries a performance penalty from increased connection churn. Where the downstream HTTP/3 listener is not required, disabling HTTP/3 termination removes the specific translation path, at the cost of losing HTTP/3 support.