britrik skill-vettr v2.0.3
Security scanner for third-party OpenClaw skills. Analyses source code, dependencies, and metadata before installation using tree-sitter AST parsing and regex pattern matching.
Installation
npm install
This installs all Node.js dependencies, including tree-sitter .wasm grammar files required at runtime for AST-based analysis. The .wasm files are located in node_modules and must be present for the skill to function.
⚠️ Install safety:
npm installruns dependency lifecycle scripts, which can execute arbitrary code. For stronger isolation, runnpm ci --ignore-scripts— but note that tree-sitter native/WASM artifacts may not build, breaking AST analysis. Prefer installing inside a container or VM when possible.
External Binaries
The vet-url and vet-clawhub commands invoke external binaries via execSafe (which uses execFile — no shell is spawned). Only the following commands are permitted:
| Binary | Used By | Purpose |
|---|---|---|
git |
vet-url |
Clone .git URLs (with hooks disabled) |
curl |
vet-url |
Download archive URLs |
tar |
vet-url |
Extract downloaded archives |
clawhub |
vet-clawhub |
Fetch skills from ClawHub registry |
The /skill:vet command (local path vetting) requires only node and no external binaries.
Commands
/skill:vet --path <directory>— Vet a local skill directory/skill:vet-url --url <https://...>— Download and vet from URL/skill:vet-clawhub --skill <slug>— Fetch and vet from ClawHub
Detection Categories
| Category | Method | Examples |
|---|---|---|
| Code execution | AST | eval(), new Function(), vm.runInThisContext() |
| Shell injection | AST | exec(), execSync(), spawn("bash"), child_process imports |
| Dynamic require | AST | require(variable), require(templateString) |
| Prototype pollution | AST | proto assignment |
| Prompt injection | Regex | Instruction override patterns, control tokens (in string literals) |
| Homoglyph attacks | Regex | Cyrillic/Greek lookalike characters in identifiers |
| Encoded names | Regex | Unicode/hex-escaped "eval", "exec" |
| Credential paths | Regex | Cloud and SSH credential directory references, system credential store access |
| Network calls | AST | fetch() with literal URLs (checked against allowlist) |
| Malicious deps | Config | Known bad packages, lifecycle scripts, git/http deps |
| Typosquatting | Levenshtein | Skill names within edit distance 2 of targets |
| Dangerous permissions | Config | shell:exec, credentials:read in SKILL.md |
Limitations
⚠️ This is a heuristic scanner with inherent limitations. It cannot guarantee safety.
- Static analysis only — Cannot detect runtime behaviour (e.g., code that fetches malware after install)
- Evasion possible — Sophisticated obfuscation or multi-stage string construction can evade detection
- JS/TS only — Binary payloads, images, and non-text files are skipped
- Limited network detection — Only detects
fetch()with literal URL strings; misses axios, http module, dynamic URLs - No sandboxing — Does not execute or isolate target code
- Comment scanning — Prompt injection detection scans string literals, not comments
- Filesystem scope —
vet-urldownloads and extracts remote archives into a temp directory;vetaccepts paths underos.tmpdir(),~/.openclaw, and~/Downloadsby default. SetallowCwd: truein config to also permitprocess.cwd()(see Configuration below) - External binary trust —
vet-urlandvet-clawhubinvokegit,curl,tar, andclawhubviaexecFile. These binaries must be trusted and present onPATH
For high-security environments, combine with sandboxing, network isolation, and manual source review. Run inside a disposable container when vetting untrusted URLs.
Configuration
allowCwd
By default, process.cwd() is not included in the set of allowed vetting roots. The default allowed roots are:
os.tmpdir()~/.openclaw~/Downloads
To allow vetting paths under the current working directory, set allowCwd: true in your vetting config:
{
"allowCwd": true
}
⚠️ Security implication: Enabling
allowCwdmeans the scanner will accept any path under the directory you launched it from. If you run from/or$HOME, this effectively grants access to your entire filesystem. Only enable this when running from a scoped project directory or inside a container.
.vettrignore
Place a .vettrignore file in the root of the skill directory being scanned to exclude files or directories from analysis. This is useful for excluding test fixtures that contain deliberate malicious patterns.
Format
- One glob pattern per line
- Lines starting with
#are comments - Empty lines are ignored
- Patterns ending with
/match entire directories *matches any sequence of non-separator characters**matches any sequence including path separators (recursive)?matches a single non-separator character
Example
# Exclude test fixtures containing deliberate prompt injection vectors
test/fixtures/
# Exclude generated files
dist/
*.min.js
If the .vettrignore file is unreadable or contains invalid UTF-8, the engine logs an INFO-level warning and proceeds with a full scan.