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?

Medium severity, with a CVSS score of 6.5, published 19 May 2026.

Which products and versions are affected?

Envoy Proxy AI Gateway < 0.6.0; github.com/envoyproxy/ai-gateway (Go) < 0.6.0.

Is there a fix for This vulnerability?

A patch was published on 2026-05-19: Version 0.6.0 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is This vulnerability attacked?

It is attacked over the network, in a software library.

Check whether you run Envoy Proxy AI Gateway or 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.

Envoy AI Gateway MCP message smuggling via parser differential

Q: Is there a fix for This vulnerability?

A patch was published on 2026-05-19: Version 0.6.0 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is This vulnerability attacked?

It is attacked over the network, in a software library.

Q: Am I affected?

Check whether you run Envoy Proxy AI Gateway or 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.

Severity: medium · CVSS 6.5 · Published 2026-05-19

Envoy AI Gateway, a tool used to manage and route traffic to AI services, is vulnerable to a message smuggling flaw. An attacker can send specially crafted requests that bypass security filters by using inconsistent capitalization in the data. This allows unauthorized commands to be executed on backend AI systems, potentially leading to unauthorized data access or misuse of AI tools.

Technologies: github.com/envoyproxy/ai-gateway (Go). Vendors: Envoy Proxy, 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?: Medium severity, with a CVSS score of 6.5, published 19 May 2026.
Which products and versions are affected?: Envoy Proxy AI Gateway < 0.6.0; github.com/envoyproxy/ai-gateway (Go) < 0.6.0.
Is there a fix for This vulnerability?: A patch was published on 2026-05-19: Version 0.6.0 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is This vulnerability attacked?: It is attacked over the network, in a software library.
Am I affected?: Check whether you run Envoy Proxy AI Gateway or 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.

Technical details

The vulnerability arises from a parser differential between the Model Context Protocol (MCP) specification and the Go-based JSON libraries used in Envoy AI Gateway (specifically `modelcontextprotocol/go-sdk` and `bytedance/sonic`). While JSON-RPC 2.0 requires case-sensitive matching, the gateway's internal unmarshaling is case-insensitive. An attacker can provide duplicate fields with different casing (e.g., 'name' and 'Name'). The gateway validates the compliant field but may overwrite it with the malicious value from the non-compliant field during internal processing. When the gateway re-serializes the message for the upstream backend, it produces a valid, canonicalized JSON-RPC request containing the smuggled malicious value, effectively bypassing any intermediate authorization layers. This affects 'tools/call', 'prompts/get', and 'resources/read' message types.

Affected products

envoyproxy ai-gateway < 0.6.0

Timeline

2026-05-13: advisory: Initial GHSA disclosure
2026-05-19: patched: Version 0.6.0 released

References

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