Severity: Medium
Platforms Affected: All

Description

Skills are increasingly ported across platforms (OpenClaw → Claude Code → Cursor → VS Code) without translating the security properties of the source format. A skill with a permission manifest on one platform is stripped of that manifest on another. Security controls that exist in one ecosystem’s metadata format simply do not exist in another’s — creating exploitable gaps when skills cross platform boundaries.

Why It’s Unique to Skills

MCP standardizes the protocol. AST10 addresses the content security within skills — the fact that there is no universal skill format and no normalization of security metadata when skills are ported. This is not a protocol problem; it is a behavioral abstraction problem.

Real-World Evidence

• Snyk ToxicSkills confirmed malicious skills published simultaneously on ClawHub and skills.sh by the same threat actors (zaycv, moonshine-100rze), exploiting the fact that neither platform shared scanning intelligence.
• Snyk’s toxicskills-goof proof-of-concept demonstrates a fake Vercel skill that works across Gemini CLI and OpenClaw — the same malicious SKILL.md is effective on multiple runtimes.
• The absence of a universal format means organizations managing a multi-platform agent stack cannot apply a single governance policy — each platform requires separate tooling, separate scanning, and separate approval workflows.

Attack Scenarios

Security Property Loss in Translation

A skill with risk_tier: L3 (destructive) is ported to a platform that doesn’t support risk_tier; the warning is silently dropped.

Cross-Registry Arbitrage

Attacker publishes a skill on a lightly-scanned registry (skills.sh) and promotes it to a more-trusted registry, leveraging the install count as a false trust signal.

Multi-Platform Campaign

Same malicious payload deployed across four platforms simultaneously; security teams on each platform are unaware of the others’ incidents.

Preventive Mitigations

1. Adopt the Universal Skill Format (see below) for all new skill development.
2. When porting skills across platforms, require a full security metadata re-validation — never assume equivalence.
3. Establish cross-registry threat intelligence sharing between major skill registries.
4. Build platform-agnostic skill scanners that evaluate the content layer independently of the runtime.
5. Normalize risk_tier, permissions, and signature fields across all platform-specific formats.

Tooling: metadata loss simulator

Use the browser-only Cross-platform metadata loss simulator to paste a source manifest and a ported target manifest (YAML or JSON). It normalizes fields, highlights lost or weakened security properties (for example allowlisted egress replaced by network: true), and exports a machine-readable JSON report suitable for PRs or ticket evidence.

Universal Skill Format Proposal

The following YAML format is proposed as a cross-platform standard that mitigates AST10 and provides the metadata foundation required to address AST01 through AST09. It is designed to be a superset of all current platform-specific formats.

---
# Universal Agentic Skill Format v1.0
# Compatible with: OpenClaw, Claude Code, Cursor/Codex, VS Code

name: example-skill
version: 1.0.0
platforms: [openclaw, claude, cursor, vscode]

description: "Safe example skill — concise, honest statement of function"
author:
  name: "Author Name"
  identity: "did:web:example.com"         # Decentralized identity anchor
  signing_key: "ed25519:pubkey_hex_here"

permissions:
  files:
    read:
      - ~/.config/app.json                 # Explicit paths only; no wildcards
    write:
      - ~/.config/app.json
    deny_write:
      - SOUL.md
      - MEMORY.md
      - AGENTS.md                          # Identity files require explicit grant
  network:
    allow:
      - api.example.com                    # Domain allowlist, not binary on/off
    deny: "*"                              # Default deny all other egress
  shell: false                             # Explicit shell access declaration
  tools:
    - web_fetch
    - read_file

requires:
  binaries: [jq, curl]
  min_runtime_version: "2026.1.0"

risk_tier: L1                              # L0=safe, L1=low, L2=elevated, L3=destructive
scan_status:
  scanner: "[email protected]"
  last_scanned: "2026-02-15"
  result: "pass"

signature: "ed25519:ABCDEF1234567890..."   # Signs the canonical hash of this manifest
content_hash: "sha256:abcdef1234..."       # Hash of the complete skill package

changelog:
  - version: "1.0.0"
    date: "2026-02-01"
    notes: "Initial release"
---

Format design rationale:

• permissions.deny_write protects identity files (SOUL.md, MEMORY.md) by default — must be explicitly overridden.
• network.allow is a domain allowlist, not a boolean — closing the “network: true” over-permission gap (AST03).
• signature and content_hash together enable Merkle-root registry verification (AST01/AST02).
• scan_status creates a machine-readable provenance trail (AST08/AST09).
• risk_tier enables automated governance policies without per-skill review (AST09/AST10).

OWASP Mapping

• LLM03 (Supply Chain)
• CWE-1357 (Reliance on Insufficiently Trustworthy Component)

MAESTRO Framework Mapping

MAESTRO Layer Details

• Layer 7: Agent Ecosystem - cross-registry incident sharing, false trust signals.
• Layer 3: Agent Frameworks - framework-level normalization of security metadata.
• Layer 6: Security & Compliance - cross-platform governance for skill attributes.

Cross-References

• AST01 (Malicious Skills): Cross-platform reuse allows malicious skills to spread across ecosystems.
• AST02 (Supply Chain Compromise): Compromised skills can be reused across platforms.
• AST04 (Insecure Metadata): Inconsistent metadata formats create confusion and exploitation.
• AST08 (Poor Scanning): Skills may pass scanning on one platform but be vulnerable on another.
• AST09 (No Governance): Lack of cross-platform governance enables skill proliferation.

References

• Snyk ToxicSkills
• Snyk: toxicskills-goof
• OWASP MCP Top 10

Last updated: March 2026