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Security audit

Fastmail API

Security checks across malware telemetry and agentic risk

Overview

This skill is a high-impact Fastmail automation guide, but its network use, local storage, credential handling, and destructive-operation safeguards are mostly disclosed and purpose-aligned.

Install only if you are comfortable giving an agent a Fastmail API token with the scopes needed for your task. Use the narrowest token scope, review the files under ~/Clawic/data/fastmail-api/ and shared Clawic boxes periodically, and pay close attention to confirmations for sending, destroying, mailbox changes, contact merges, and calendar events with participants.

SkillSpector

Vulnerability Patterns
  • Rogue AgentSelf-Modification, Session Persistence
  • MCP Tool PoisoningHidden Instructions, Unicode Deception, Parameter Description Injection
  • Prompt InjectionInstruction Override, Hidden Instructions, Exfiltration Commands
  • Data ExfiltrationExternal Transmission, Env Variable Harvesting, File System Enumeration
  • Privilege EscalationExcessive Permissions, Sudo/Root Execution, Credential Access
Findings (2)

Intent-Code Divergence

Medium
Confidence
95% confidence
Finding
The skill states that 'nothing leaves the machine' immediately after describing local reads/writes, but the skill later instructs authenticated API calls to Fastmail. This is a misleading security/privacy claim that can cause users or downstream agents to underestimate data egress and approve actions they would otherwise scrutinize. In this context, the skill handles mail, contacts, calendars, and tokens, so inaccurate disclosure materially increases privacy and authorization risk.

Session Persistence

Medium
Category
Rogue Agent
Content
## Start flat, split only when it hurts

Everything except artifacts, snapshots, operation logs and the shared boxes begins inside `memory.md`. Splitting is a procedure carried out by whichever agent is about to write the entry that crosses the threshold — never deferred, never proposed to the user:

1. Before appending to a section, count its entries.
2. If the append would take it past **~15 entries or ~40 lines of real content** — scaffolding, headings and comments do not count — then, in the same turn: create the new file in `~/Clawic/data/fastmail-api/`, move the whole section into it, **delete the section from `memory.md`**, add its line to `## Boxes`, and append the new entry to the new file.
Confidence
88% confidence
Finding
The skill directs the agent to persist a broad range of observed account metadata and operational history across sessions without user confirmation. Even though it excludes raw secrets, the stored data includes mailbox mappings, identities, aliases, masked emails, contacts, booking details, and operation logs, which can accumulate sensitive personal and organizational context and increase privacy risk if the workspace is exposed or over-retained.

VirusTotal

64/64 vendors flagged this skill as clean.

View on VirusTotal

Static analysis

Detected: suspicious.exposed_secret_literal

File appears to expose a hardcoded API secret or token.

Critical
Code
suspicious.exposed_secret_literal
Location
memory-template.md:71