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Security audit

Fern

Security checks for vulnerabilities and agentic risk

Overview

The Fern reader needs review because its fallback setup executes remote installation code without clearly limiting or reviewing the resulting changes.

Install and review the CLI separately before allowing this skill to run, including any automatic changes to other agents' skills. Use narrowly scoped Fern credentials and understand that OOMOL handles the requested financial data. The complete bundled artifact was inspected, but remote installer behavior remains unverified; no malicious behavior 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
  • Output HandlingUnvalidated Output Injection, Cross-Context Output, Unbounded Output
  • MCP Tool PoisoningHidden Instructions, Unicode Deception, Parameter Description Injection
  • Prompt InjectionInstruction Override, Hidden Instructions, Exfiltration Commands
Findings (4)

Description-Behavior Mismatch

High
Category
MCP Tool Poisoning
Confidence
99% confidence
Finding

The supplied command runs an Oomol-hosted installer rather than searching or reading Fern data. Nothing in the supplied chunk establishes this installer as a supporting dependency for Fern access. Remote installer execution is a materially different, undeclared capability. The fetched script's contents and any further effects cannot be determined from this chunk.

Content

No source excerpt is available for this finding.

External Script Fetching

High
Category
Supply Chain
Confidence
98% confidence
Finding

The installation command executes a remotely fetched, unpinned script immediately, without an integrity check or opportunity to review it; the PowerShell alternative has the same issue. If the distribution infrastructure is compromised, the script could access local credentials or modify files with the invoking user's privileges, although HTTPS and the conditional setup path reduce some exposure.

Content

Scanner excerpt · SKILL.md (reported line 61)May include surrounding context.

The fallback setup instructs the agent to execute a remote installer without warning the user about system changes.

Medium
Category
Output Handling
Confidence
96% confidence
Finding

A missing CLI triggers instructions to install software without first obtaining approval for local system changes. A request to read Fern data does not inherently authorize software installation, although restricting this fallback to a missing dependency reduces its exposure.

Content

No source excerpt is available for this finding.

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 82)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