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Security audit

Cal.com

Security checks for vulnerabilities and agentic risk

Overview

The calendar functions have clear approval controls, but setup directs the agent to execute an unverified remote installer without separate approval.

Review and approve the CLI installation separately, using a pinned release with independently verified integrity. Check its automatic skill synchronization before allowing it to modify agent configuration. OOMOL will mediate access to your connected calendar account. Calendar changes require confirmation, but the remote installers and hosted implementation remain unverified; no malicious payload was established.

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
Vulnerability Patterns
  • Supply ChainUnpinned Dependencies, External Script Fetching, Obfuscated Code
  • Excessive AgencyUnrestricted Tool Access, Autonomous Decision Making, Scope Creep
  • 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
Findings (3)

Description-Behavior Mismatch

High
Category
MCP Tool Poisoning
Confidence
96% confidence
Finding

The supplied code performs remote software installation rather than any Cal.com operation. Although dependency installation can be a supporting implementation detail, this chunk provides no evidence connecting the Oomol installer to the declared Cal.com functionality. The downloaded script's contents and further effects are not available for assessment.

Content

No source excerpt is available for this finding.

External Script Fetching

High
Category
Supply Chain
Confidence
98% confidence
Finding

The setup instructions pipe a remotely fetched, unpinned script directly into Bash without independent integrity verification; the PowerShell alternative uses the same download-and-execute pattern. If the distribution endpoint or release pipeline is compromised, attacker-controlled code executes with the agent process's permissions and could access local files or credentials. The missing-CLI condition limits exposure, but HTTPS and server-side Cal.com credential handling do not eliminate this local execution risk.

Content

Scanner excerpt · SKILL.md (reported line 101)May include surrounding context.

Autonomous Decision Making

Medium
Category
Excessive Agency
Confidence
80% confidence
Finding

Skill enables autonomous high-impact decisions without human-in-the-loop verification. Critical operations (destructive commands, financial transactions, data deletion) should require explicit user confirmation.

Content

Scanner excerpt · SKILL.md (reported line 122)May include surrounding context.

md
- **`OOMOL_INSUFFICIENT_CREDIT`** — OOMOL billing stop. Recharge at `https://console.oomol.com/billing/token-recharge` before retrying.

- **HTTP 402 without `OOMOL_INSUFFICIENT_CREDIT`** — the third-party account itself has no active plan or credit. Report the provider error message as is; do not ask the user to recharge OOMOL.

## Resources