wasm_instrument_binary
Real wasm-level binary instrumentation: disassembles via wasm2wat, inserts a call to an imported trace function at every function entry, and reassembles via wat2wasm. Unlike wasm_instrument_trace (which only proxies JS-visible exports), this rewrites the code section so every function entry is ob...
This record as markdown: /tools/io-github-vmoranv-jshookmcp/wasm-instrument-binary.md
What wasm_instrument_binary does on Jshookmcp
AI agents invoke wasm_instrument_binary to trigger actions in Jshookmcp. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.
Why wasm_instrument_binary is rated High
Modifies and reassembles WASM binaries by instrumenting code sections, executing binary transformation.
From the tool's definition disassembles, inserts call, rewrites code section, reassembles binary
Risk signalsBulk/mass operation — affects multiple targets
Attacks that exploit this kind of access
The rule that runs wasm_instrument_binary safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Jshookmcp, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For wasm_instrument_binary, this is the rule to start with:
wasm_instrument_binary stays usable, but rate-capped: a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Jshookmcp, apply this rule, and every wasm_instrument_binary call is checked against it from then on.
Questions about wasm_instrument_binary
Real wasm-level binary instrumentation: disassembles via wasm2wat, inserts a call to an imported trace function at every function entry, and reassembles via wat2wasm. Unlike wasm_instrument_trace (which only proxies JS-visible exports), this rewrites the code section so every function entry is observable. Honest boundary: function-ENTRY-level tracing, not basic-block — the host must supply the trace_fn import at instantiation. It is categorised as a Execute tool in the Jshookmcp MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Jshook MCP server in PolicyLayer and add a rule for wasm_instrument_binary: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Jshookmcp. Nothing to install.
wasm_instrument_binary is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the wasm_instrument_binary rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for wasm_instrument_binary. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
wasm_instrument_binary is provided by the Jshook MCP server (@jshookmcp/jshook). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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