# GO-2026-5121 - Envoy AI Proxy - MCP Message Smuggling Vulnerability in github.com/envoyproxy/ai-gateway

Source: https://junglewise.ai/threats/go-2026-5121-envoy-ai-proxy-mcp-message-smuggling-vulnerability-in-a34cd851  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-25  
License: CC BY 4.0 with a link back

Severity: info · Published 2026-06-25

Envoy AI Proxy - MCP Message Smuggling Vulnerability in github.com/envoyproxy/ai-gateway

Technologies: [github.com/envoyproxy/ai-gateway (Go)](https://junglewise.ai/threats/technologies/github-com-envoyproxy-ai-gateway). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Informational severity, published 25 June 2026.

**Which products and versions are affected?** github.com/envoyproxy/ai-gateway (Go) SEMVER:introduced=0,fixed=0.6.0.

**Is there a fix for This vulnerability?** Yes. github.com/envoyproxy/ai-gateway (Go): upgrade to 0.6.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected?** Check whether you run github.com/envoyproxy/ai-gateway (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/envoyproxy/ai-gateway (Go): upgrade to 0.6.0 or later

  ```sh
  go get github.com/envoyproxy/ai-gateway@v0.6.0
  ```


## Affected products

- github.com/envoyproxy/ai-gateway (Go) SEMVER:introduced=0,fixed=0.6.0

## Related threats

- [Envoy AI Gateway MCP session hijacking via missing subject verification](https://junglewise.ai/threats/agent-router-mcp-session-resume-does-not-verify-the-embedded-anti-4b0a70ec)
- [Envoy AI Gateway MCP message smuggling via parser differential](https://junglewise.ai/threats/envoy-ai-gateway-mcp-message-smuggling-via-parser-differential-a56e7319)