POC Walkthrough — cors (npm)

Last updated: 2026-05-24

The cors package is the canonical CVE-history walkthrough in the CleanLibrary POC. It demonstrates how the verdict shifts across versions when a known vulnerability is introduced and subsequently patched — the DENY → ALLOW upgrade-path Quick-Fix workflow that defines CleanLibrary's value at the developer's point of install.

Versions covered

Version	Decision	Severity	Reasoning
2.8.0	ALLOW	None	Healthy older release; no findings
2.8.1	ALLOW	None	Healthy
2.8.4	DENY	High	Prototype pollution vulnerability; upgrade to 2.8.5 patched release
2.8.5	ALLOW	None	Patched; recommended upgrade target from 2.8.4
2.8.6	ALLOW	None	Current; widely deployed

1. Query a verdict directly

$ curl -sH "Authorization: Bearer your-poc-key" \
  https://cleanapp.clnstrt.dev/v1/customer/verdicts/npm/cors/2.8.4 | jq

{
  "verdict_id": "01KDVDNA0000000000000001YK",
  "verdict": "VECTOR_VERDICT",
  "source": "VECTOR_VERDICT",
  "confidence": 0.98,
  "composite_score": 78,
  "severity": "HIGH",
  "reasoning": "Prototype pollution vulnerability in cors 2.8.4; upgrade to 2.8.5 patched release",
  "suggested_actions": [
    "Upgrade to cors@2.8.5 or later",
    "Audit downstream consumers for prototype pollution exposure"
  ],
  ...
}

Then check the patched version:

$ curl -sH "Authorization: Bearer your-poc-key" \
  https://cleanapp.clnstrt.dev/v1/customer/verdicts/npm/cors/2.8.5 | jq .verdict

"ALLOWED_NO_FINDINGS"

2. VS Code extension flow

Open VS Code with the CleanLibrary extension installed:

1. Configure cleanlib.endpoint = https://cleanapp.clnstrt.dev + cleanlib.apiKey = <your key> in Settings
2. Run CleanLibrary: Fetch verdict for package (Command Palette: Ctrl/Cmd+Shift+P)
3. Select ecosystem: npm
4. Package name: cors
5. Version: 2.8.4

Expected: Inline notification with red icon, DENY, and the Quick Fix shown in the detail pane — actionable at the developer's point of install.

Then repeat with version 2.8.5:

Expected: Green icon, ALLOW, healthy.

3. Python SDK flow

from cleanlib_sdk import CleanlibClient

client = CleanlibClient(
    endpoint="https://cleanapp.clnstrt.dev",
    api_key="your-poc-key",
)

vulnerable = client.fetch_verdict("npm", "cors", "2.8.4")
print(f"{vulnerable.decision}: {vulnerable.reasoning}")
# DENY: Prototype pollution vulnerability in cors 2.8.4; upgrade to 2.8.5 patched release

patched = client.fetch_verdict("npm", "cors", "2.8.5")
print(f"{patched.decision}: {patched.reasoning}")
# ALLOW: CORS middleware; prototype pollution patched; recommended upgrade target from 2.8.4

4. Go SDK flow

import cleanlibsdk "pkg.clnstrt.dev/cleanlib-sdk-go"

client, _ := cleanlibsdk.NewClient(
    "https://cleanapp.clnstrt.dev",
    cleanlibsdk.WithAPIKey("your-poc-key"),
)

ctx := context.Background()
vulnerable, _ := client.FetchVerdict(ctx, "npm", "cors", "2.8.4")
fmt.Printf("%s: %s\n", vulnerable.Decision, vulnerable.Reasoning)
// DENY: Prototype pollution vulnerability in cors 2.8.4; upgrade to 2.8.5 patched release

patched, _ := client.FetchVerdict(ctx, "npm", "cors", "2.8.5")
fmt.Printf("%s: %s\n", patched.Decision, patched.Reasoning)
// ALLOW: CORS middleware; prototype pollution patched

5. JS/TS SDK flow

import { CleanlibClient } from "@cleanstart/cleanlib-sdk";

const client = new CleanlibClient("https://cleanapp.clnstrt.dev", {
  apiKey: "your-poc-key",
});

const vulnerable = await client.fetchVerdict("npm", "cors", "2.8.4");
console.log(`${vulnerable.decision}: ${vulnerable.reasoning}`);
// VECTOR_VERDICT: Prototype pollution vulnerability in cors 2.8.4; upgrade to 2.8.5

const patched = await client.fetchVerdict("npm", "cors", "2.8.5");
console.log(`${patched.decision}: ${patched.reasoning}`);
// ALLOWED_NO_FINDINGS: prototype pollution patched

6. MCP server flow (Claude Desktop / Cursor / Windsurf / Cline)

Configure your MCP client per the MCP Server reference. Then in your AI conversation:

You: Get the CleanLibrary verdict for npm cors 2.8.4
AI:  [calls cleanlib_fetch_verdict tool]
     ✗ npm/cors@2.8.4 → DENY (confidence 98%)
     Reasoning: Prototype pollution vulnerability in cors 2.8.4; upgrade to 2.8.5 patched release.
     Suggested actions: Upgrade to cors@2.8.5 or later; Audit downstream consumers.

You: What about 2.8.5?
AI:  [calls cleanlib_fetch_verdict tool]
     ✓ npm/cors@2.8.5 → ALLOW (confidence 96%)
     Reasoning: CORS middleware; prototype pollution patched.

7. What this walkthrough validates

Capability	Demonstrated by cors
Verdict accuracy on a known CVE	2.8.4 returns DENY with High severity matching public CVE record
Verdict shift across versions	2.8.4 DENY → 2.8.5 ALLOW matches the actual patched-release boundary
Actionable Quick Fix recommendations	suggested_actions includes specific upgrade target + downstream-audit guidance
Workflow integration	Same verdict returned consistently across VS Code + SDKs + MCP + curl
Confidence signal	High-confidence DENY for known CVE (0.98) vs high-confidence ALLOW for patched (0.96)

8. What to look for during evaluation

• Does the DENY trigger when you try to use cors 2.8.4 in your dependency manifest?
• Is the Quick Fix actionable for your team — would you actually apply it?
• Does the verdict round-trip preserve fidelity across your tooling (CLI, IDE, AI agent, audit log)?
• Is the latency acceptable for your developer's interactive use case? (p95 <200ms target for in-cache verdicts)

Feedback channel: see API Key Onboarding §7.