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Security audit

UK Tax Calculator & MTD Prep

Security checks for vulnerabilities and agentic risk

Overview

This is a disclosed UK freelancer tax estimate skill with no executable code, persistence, credential use, or hidden data access, though users should treat outputs as estimates rather than tax advice.

Use this for planning estimates only. Verify rates, thresholds, edge cases, and filing obligations with HMRC or a qualified accountant before relying on the numbers for returns, VAT registration, MTD submissions, or payment timing.

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
  • Trigger AbuseOverly Broad Trigger, Shadow Command Trigger, Keyword Baiting Trigger
  • Prompt InjectionInstruction Override, Hidden Instructions, Exfiltration Commands
  • Data ExfiltrationExternal Transmission, Env Variable Harvesting, File System Enumeration
  • Privilege EscalationExcessive Permissions, Sudo/Root Execution, Credential Access
  • Supply ChainUnpinned Dependencies, External Script Fetching, Obfuscated Code
Findings (2)

Vague Triggers

Medium
Confidence
94% confidence
Finding
The skill metadata and description are broad enough to trigger on general UK tax, VAT, self-assessment, NI, and MTD questions, which can cause over-invocation outside a narrowly scoped calculator workflow. In an agent system, this increases the chance that the skill is selected for ambiguous financial conversations and may provide authoritative-seeming tax guidance where a simple estimate tool is not the safest or most appropriate handler.

Missing User Warnings

Medium
Confidence
96% confidence
Finding
The listing presents the calculator as 'complete' and 'accurate' using 'verified 2025/26 HMRC rates' without any visible disclaimer that results are informational only and may not substitute for professional tax advice or official HMRC calculations. In a tax context, users may reasonably rely on the output for filings, reserves, VAT registration timing, or Payment on Account decisions, creating financial and compliance risk if rates, thresholds, or user inputs are wrong.

Static analysis

No suspicious patterns detected.