Envoy AI Proxy - MCP Message Smuggling Vulnerability

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.3 · CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Envoy AI Gateway was found to be affected by a protocol parser differential vulnerability due to improper implementation of the JSON-RPC 2.0 specification. Such differential causes a MCP message alteration, potentially causing a bypass of security controls in a multi-layered architecture. According to the JSON RPC Spec used by Model Context Protocol, JSON RPC should be case sensitive https://www.jsonrpc.org/specification The AI Gateway is accepting and processing case-variant fields that compliant MCP implementations correctly ignore. Crucially, Envoy does not just "pass through" the message by acting as a transparent proxy, it alters the traffic, allowing smuggling of unwanted requests. The following steps represent the incoming message alteration: 1. Incoming MCP Message: 2. Parses the request, picking the non-standard Name field over the authorized name field due to internal case-insentitive parsing by libraries such as modelcontextprotocol/go-sdk/jsonrpc and…

Published by the source

19 May 2026, 16:18 UTC

Last modified by the source

19 May 2026, 16:18 UTC

Source last checked

26 Oct 2026, 15:22 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-4gph-2hhr-5mwg

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# Patch Next advisory brief: GHSA-4gph-2hhr-5mwg

Advisory: Envoy AI Proxy - MCP Message Smuggling Vulnerability
IDs: GHSA-4gph-2hhr-5mwg
Record: https://patchnext.com/advisories/ghsa-4gph-2hhr-5mwg (revision 1, source checked 26 Oct 2026, 15:22 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/envoyproxy/ai-gateway 0.6.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/envoyproxy/ai-gateway: affected < 0.6.0; fixed in 0.6.0

## Suggested inspection (read-only)
- Go github.com/envoyproxy/ai-gateway: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/envoyproxy/ai-gateway.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-4gph-2hhr-5mwg (GitHub-reviewed advisory GHSA-4gph-2hhr-5mwg lists affected ranges: Go github.com/envoyproxy/ai-gateway >=0 <0.6.0)

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