Security audit

singapore-stamp-duty-calculator

Security checks for vulnerabilities and agentic risk

Overview

This narrowly scoped calculator openly sends three calculation inputs to an external service and requires approval for paid follow-ups.

The external service receives the property value, buyer category, and property count; the skill does not explain retention practices. Share only those inputs, verify estimates with IRAS, and review any paid follow-up before approving it.

A.I.G

Vulnerability Patterns

Skill Instruction HijackingAlters the agent's session goals or safety constraints when the skill loads
Agent Memory PoisoningWrites attacker-controlled rules into memory that affect later sessions
Remote Payload Retrieval and ExecutionFetches external code whose behavior can change after review
Embedded Malicious CodeShips malicious scripts inside the skill and executes them locally
Unauthorized Access and Privilege EscalationObtains permissions beyond the task's legitimate needs

SkillSpector

Vulnerability Patterns

Data ExfiltrationExternal Transmission, Env Variable Harvesting, File System Enumeration
Output HandlingUnvalidated Output Injection, Cross-Context Output, Unbounded Output
Prompt InjectionInstruction Override, Hidden Instructions, Exfiltration Commands
Privilege EscalationExcessive Permissions, Sudo/Root Execution, Credential Access
Supply ChainUnpinned Dependencies, External Script Fetching, Obfuscated Code

Findings (2)

External Transmission

Medium

Category: Data Exfiltration
Confidence: 60% confidence
Finding: Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.
Content: Scanner excerpt · SKILL.md (reported line 14)May include surrounding context.
How to run

sh
curl -s -X POST https://finch-agent-catalog.finch-catalog-mcp.workers.dev/mcp \ -H 'Content-Type: application/json' -H 'Accept: application/json, text/event-stream' \ -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"calculate_singapore_stamp_duty","arguments":{"price_sgd":1500000,"buyer":"pr","property_count":1}}}'

The calculator transmits property and buyer information to a third-party service without a privacy warning.