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Show HN: VellaVeto — blocks unsafe MCP tool calls by default (github.com)

2 points by paolovella ↗ HN
Reposting because the March thread linked a now-outdated repo, and the project has changed substantially.

VellaVeto is a fail-closed gateway between an AI agent and its MCP tools. Every tool call is evaluated before execution; if evaluation fails for any reason, the call is denied.

Concrete example: under shield mode, a filesystem server trying to read ~/.ssh/id_rsa is denied by default. A list_files /tmp call from the same server is allowed.

What it does not solve: prompt injection, model-level jailbreaks, or supply-chain attacks in server packages. It only controls what crosses the tool-call boundary.

Since March, I added three zero-config protection levels, topology discovery, tamper-evident audit, Consumer Shield, and MCPSEC, an open benchmark for MCP gateways.

The feedback I’d most like:

Is the tool-call boundary the right place to enforce MCP security? Are the MCPSEC attack classes sensible? What important attack classes am I still missing?

3 comments

[ 2.8 ms ] story [ 19.4 ms ] thread
bettaher_adam
The fail-closed approach is the right default. One thing I'd add to the attack classes you're considering: prompt injection via filesystem reads — an attacker can craft a file that, when read by the agent, injects instructions into the tool-call chain.

We solved a similar boundary problem by signing all outputs with HMAC-SHA256 so downstream consumers can verify the response wasn't modified after the tool-call boundary. Not a replacement for your approach but complementary — input validation + output signing covers both ends.

Is the MCPSEC benchmark public yet?