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

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

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

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

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. …

Unlock full vulnerability intelligence

Risk assessment & exploitation conditions
Attack chain visualization
Remediation with exact patch versions
Threat intelligence from 22 sources
Personal watchlist & email alerts

Continue with Google Continue with GitHub

Free forever · No credit card required

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access

Reach Envoy HTTP/3 listener

Delivery

Send FIN-complete request with nonzero Content-Length

Exploit

Envoy emits HTTP/1 upstream request with body debt

Execution

Smuggled bytes consumed as next request by origin

Persist

Origin parses injected GET /pwn

Impact

Route/authorization bypass response returned to attacker

Access

Reach Envoy HTTP/3 listener

Delivery

Send FIN-complete request with nonzero Content-Length

Exploit

Envoy emits HTTP/1 upstream request with body debt

Execution

Smuggled bytes consumed as next request by origin

Persist

Origin parses injected GET /pwn

Impact

Route/authorization bypass response returned to attacker

Vulnerability AssessmentAI

Exploitation	Exploitation requires Envoy deployed with a downstream HTTP/3 listener forwarding to an HTTP/1 (HTTP/1.1) upstream, and an origin server that replies before reading the declared request body while keeping the connection reusable (keep-alive). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment	The vendor CVSS:3.1 vector (AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N, base 7.5) reflects a network-reachable, unauthenticated attack with high complexity, a scope change (Envoy desyncs a separate backend connection), high integrity impact (request injection/route bypass), low confidentiality impact, and no availability impact - a coherent profile for a smuggling/desync bug. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	An attacker sends a crafted HTTP/3 request to an Envoy listener that is headers-only/FIN-complete but declares a nonzero Content-Length, causing Envoy to emit an HTTP/1 request with an unsatisfied body to a reusable upstream connection. Because the origin answers before reading the body, the attacker's smuggled bytes (e.g. …
Remediation	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). … Detailed patch versions, workarounds, and compensating controls in full report.