aeon-skill-security-scan

Skills tell agents what to do. A malicious or sloppy skill can shell-inject, exfiltrate secrets, override instructions, or run destructive commands. This skill scans every installed SKILL.md and companion script and surfaces the risks before they execute.

Scope

• <skills-dir>/*/SKILL.md — primary.
• <skills-dir>/*/scripts/*.sh and *.py — companion scripts.
• <skills-dir>/*/references/* — documents loaded at runtime.

Default <skills-dir> is the current working directory.

Threat patterns

| Category | What it looks like | |---|---| | Shell injection | Unquoted variable expansion, eval, backticks, $(...) with user data. | | Secret exfiltration | Env vars or file contents piped to outbound HTTP. | | Path traversal | ../.. chains, absolute paths reaching outside the skill dir. | | Prompt override | "Ignore previous instructions", persona swaps, instructions inside fetched content. | | Destructive commands | Recursive deletes rooted at / or ~, device writes. | | Obfuscation | U+200B / U+FEFF / U+202E (Trojan Source), base64-decode-into-shell, SSRF hosts (ngrok, interact.sh, webhook.site, pipedream). |

Processing

1. Pattern scanner produces matches {file, line, pattern, severity}.
2. Code-fence downgrade — matches inside fenced code blocks drop one tier. Real run: blocks are never downgraded.
3. Baseline suppression — drop (file, pattern, line) tuples in scan-baseline.yml.
4. Trusted-publisher filter — entries in trusted-publishers.txt get format-only validation. Opt-in only.
5. Delta vs scan-state.json — fingerprint by sha256(file + line_content + pattern). Classify NEW / RESOLVED / PERSISTENT.

Per-finding remediation

| Pattern | Fix | |---|---| | eval / backticks / $(...) with variable | Quote the variable; replace eval with a function. | | curl with secret in URL | Move secret into prefetch script; never interpolate into shell. | | Path traversal | Allow-list validation; reject absolute paths. | | Prompt override phrasing | Documentation → baseline suppression; payload → delete the skill. | | Recursive delete rooted at / or ~ | Scope to the skill's own working directory. | | Obfuscation | Delete unless documented and reviewed. |

Output

Verdict CLEAN / ATTENTION / DEGRADED. Needs-attention section per NEW HIGH with one-line remediation. Resolved-since-last-scan section. Per-skill PASS / WARN / FAIL.

Written only when NEW, RESOLVED, or any current HIGH findings.

Rules

• Never auto-deletes a baseline suppression.
• Never edits the pattern library from inside the skill.
• Never notifies on a pure no-op week.
• Read-only scanning.