Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/cxcscmu/skilllearnbench/druid-javascript-securitynpx skills add cxcscmu/SkillLearnBench --skill druid-javascript-securitygit clone --depth 1 https://github.com/cxcscmu/SkillLearnBenchWhat it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00024 | $0.00628 |
| Opus 5 | $0.00012 | $0.00314 |
| Sonnet 5 | $0.00005 | $0.00126 |
| Haiku 4.5 | $0.00002 | $0.00063 |
Grade A, and why
druid-javascript-security scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 102 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Apache Druid JavaScript Security
Vulnerability Context
Apache Druid versions up to 0.20.0 have a critical vulnerability in JavaScript expression handling where an empty key ("") can bypass security settings, allowing arbitrary code execution through the java.lang.Runtime API.
Key Components
1. JavaScript Transform Spec
- Located in indexing service modules
- Handles JavaScript expressions for data transformation
- Uses GraalVM or Nashorn engine for JavaScript execution
2. Security Filter Structure
The vulnerable structure looks like:
{
"filter": {
"type": "javascript",
"function": "function(){...}",
"": {
"enabled": true
}
}
}
The empty key "" is the bypass vector.
Patching Strategy
1. Input Validation
- Reject filter/transform specs with empty string keys
- Validate all keys in security configuration objects
- Enforce strict schema validation before passing to JavaScript engine
2. Security Configuration Enforcement
- Ensure
enabledflag is only checked for known, valid keys - Implement whitelist of allowed configuration keys
- Reject any configuration with unexpected keys
3. Code Changes Needed
- Typically in classes handling JavaScript filter/transform deserialization
- Common classes:
JavaScriptFilter,JavaScriptExpressionValidator, JavaScript spec handlers - May need to add validation in both request parsing and execution phases
Testing the Fix
Exploit Request (should fail)
POST /druid/indexer/v1/sampler
{
"type": "index",
"spec": {
"dataSchema": {
"transformSpec": {
"filter": {
"type": "javascript",
"function": "function(){java.lang.Runtime.getRuntime().exec('malicious_command');}",
"": {
"enabled": true
}
}
}
}
}
}
Legitimate Request (should work)
POST /druid/indexer/v1/sampler
{
"type": "index",
"spec": {
"dataSchema": {
"transformSpec": {
"filter": {
"type": "javascript",
"function": "function(row){return true;}"
}
}
}
}
}
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago First seen · 102 lines · 24 tokens per session scan A 3dabd4c88738
druid-javascript-security is a skill published in the GitHub repository cxcscmu/SkillLearnBench (80 stars, last pushed 1mo ago), licensed MIT. It adds 24 tokens to every session and 628 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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