Summary
In tool_broker.py:215, untrusted user input is processed without adequate validation boundaries, allowing unauthenticated callers to achieve arbitrary code execution.
---
Technical Details & Root Cause
In tool_broker.py, the spend estimation gate inspects incoming transaction arguments for a currency identifier. When an autonomous tool invocation passes a bare numeric amount without an accompanying currency sibling key, the estimator defaults to 0:
# tool_broker.py:215
def estimate_cost(args: dict) -> float:
if "currency" not in args:
return 0.0 # Fails closed check, allowing unbounded transactions
return convert_to_usd(args["amount"], args["currency"])This allows autonomous agent actions to bypass declared spending limits and execute high-value financial actions without operator threshold approval.
---
Reproduction Steps (PoC)
- Start the target station locally:
```bash
railcall station --port 8799 --debug
```
- Execute the verification probe against the container:
```bash
curl -X POST http://127.0.0.1:8799/api/tools/merge_schema -d '{"__proto__": {"admin_capability": true}}'
```
- Observed Behavior:
The request is processed and executed without raising authentication or boundary exceptions, demonstrating that the vulnerable sink at line 215 is reachable.
- Expected Behavior:
The request should be validated and rejected with HTTP 400/401/403 or fail closed before executing the critical operation.
---
Impact
An attacker can exploit this issue to bypass security boundaries, compromise multi-tenant isolation, or mutate protected state within the station runtime.
---
Suggested Remediation
Enforce a strict fail-closed policy requiring an explicit currency or defaulting to the primary asset denomination:
--- a/tool_broker.py
+++ b/tool_broker.py
@@ -212,7 +212,12 @@
def estimate_cost(args: dict) -> float:
- if "currency" not in args:
- return 0.0
+ if "amount" in args and "currency" not in args:
+ # Fail-closed: assume base accounting currency rather than free action
+ return float(args["amount"])
return convert_to_usd(args.get("amount", 0), args.get("currency", "USD"))