MCP Vulnerability Checker Server

Instructions

Implementation Reference

• mcp_simple_tool/tools/epss_lookup.py:17-198 (handler)

  The core handler function for the 'get_epss_score' tool. It validates the CVE ID, queries the FIRST.org EPSS API, processes the score into risk levels and percentiles, formats a detailed Markdown response with prioritization guidance, and handles various errors.
  async def get_epss_score( cve_id: str, ) -> List[types.TextContent | types.ImageContent | types.EmbeddedResource]: """ Get EPSS (Exploit Prediction Scoring System) score for a CVE. EPSS provides probability estimates of exploitation in the wild. Args: cve_id: CVE identifier in format CVE-YYYY-NNNN Returns: List of content containing EPSS score information or error messages """ # Clean up CVE ID format cve_id = cve_id.upper().strip() if not cve_id.startswith("CVE-"): cve_id = f"CVE-{cve_id}" # Validate CVE ID format (CVE-YYYY-NNNN) if not re.match(r"^CVE-\d{4}-\d{4,}$", cve_id): return [ types.TextContent( type="text", text=f"Error: Invalid CVE ID format. Expected format: CVE-YYYY-NNNN (e.g., CVE-2021-44228). Got: {cve_id}", ) ] headers = { "User-Agent": "MCP EPSS Lookup Tool v1.0", "Accept": "application/json", } try: timeout = httpx.Timeout(15.0, connect=10.0) async with httpx.AsyncClient( follow_redirects=True, headers=headers, timeout=timeout ) as client: # FIRST.org EPSS API endpoint url = f"https://api.first.org/data/v1/epss?cve={cve_id}" response = await client.get(url) response.raise_for_status() data = response.json() if data.get("status") != "OK": return [ types.TextContent( type="text", text=f"Error: EPSS API returned status: {data.get('status', 'Unknown')}", ) ] epss_data = data.get("data", []) if not epss_data: return [ types.TextContent( type="text", text=f"No EPSS score found for {cve_id}. This CVE might be too new or not in the EPSS database.", ) ] cve_epss = epss_data[0] # EPSS API returns array, we want first item # Extract EPSS information epss_score = float(cve_epss.get("epss", 0)) percentile = float(cve_epss.get("percentile", 0)) date = cve_epss.get("date", "Unknown") # Convert EPSS score to percentage and risk level epss_percentage = epss_score * 100 # Determine risk level based on EPSS score if epss_score >= 0.7: risk_level = "🔴 CRITICAL" risk_desc = "Extremely high likelihood of exploitation" elif epss_score >= 0.3: risk_level = "🟠 HIGH" risk_desc = "High likelihood of exploitation" elif epss_score >= 0.1: risk_level = "🟡 MEDIUM" risk_desc = "Moderate likelihood of exploitation" elif epss_score >= 0.01: risk_level = "🟢 LOW" risk_desc = "Low likelihood of exploitation" else: risk_level = "⚪ VERY LOW" risk_desc = "Very low likelihood of exploitation" # Determine percentile interpretation if percentile >= 95: percentile_desc = "Top 5% most likely to be exploited" elif percentile >= 90: percentile_desc = "Top 10% most likely to be exploited" elif percentile >= 75: percentile_desc = "Top 25% most likely to be exploited" elif percentile >= 50: percentile_desc = "Above average exploitation likelihood" else: percentile_desc = "Below average exploitation likelihood" # Format the response result = f"📊 **EPSS Vulnerability Exploit Prediction: {cve_id}**\n\n" result += f"🎯 **EPSS Score:** {epss_score:.6f} ({epss_percentage:.4f}%)\n" result += f"📈 **Percentile:** {percentile:.2f}% - {percentile_desc}\n" result += f"⚠️ **Risk Level:** {risk_level}\n" result += f"📝 **Risk Description:** {risk_desc}\n" result += f"📅 **Data Date:** {date}\n\n" result += "🔍 **Understanding EPSS Scores:**\n" result += " • EPSS predicts the probability of exploitation in the wild within 30 days\n" result += " • Scores range from 0 (0%) to 1 (100%)\n" result += ( " • Higher scores indicate higher likelihood of active exploitation\n" ) result += " • Percentile shows how this CVE ranks against all CVEs\n\n" result += "📋 **Prioritization Guidance:**\n" if epss_score >= 0.3: result += " 🚨 **URGENT:** This CVE should be prioritized for immediate patching\n" result += ( " 🛡️ Consider implementing additional monitoring and controls\n" ) elif epss_score >= 0.1: result += " ⚡ **HIGH PRIORITY:** Schedule patching within your next maintenance window\n" result += " 👀 Monitor for signs of exploitation attempts\n" elif epss_score >= 0.01: result += ( " 📋 **MEDIUM PRIORITY:** Include in regular patching cycle\n" ) result += " 📊 Continue monitoring threat landscape\n" else: result += " 🕐 **LOW PRIORITY:** Can be addressed during routine maintenance\n" result += " 📈 Monitor for changes in threat landscape\n" result += "\n📊 **Data Source:** FIRST.org Exploit Prediction Scoring System (EPSS)\n" result += "🌐 **EPSS Project:** https://www.first.org/epss/" return [types.TextContent(type="text", text=result)] except httpx.TimeoutException: return [ types.TextContent( type="text", text="Error: Request timed out while fetching EPSS score from FIRST.org.", ) ] except httpx.HTTPStatusError as e: if e.response.status_code == 404: return [ types.TextContent( type="text", text=f"EPSS score for {cve_id} not found. This CVE might be too new or not in the EPSS database.", ) ] return [ types.TextContent( type="text", text=f"Error: HTTP {e.response.status_code} error while fetching EPSS data.", ) ] except json.JSONDecodeError: return [ types.TextContent( type="text", text="Error: Invalid JSON response from EPSS API." ) ] except (ValueError, TypeError) as e: return [ types.TextContent( type="text", text=f"Error: Failed to parse EPSS score data: {str(e)}", ) ] except Exception as e: return [ types.TextContent( type="text", text=f"Error: Failed to fetch EPSS information: {str(e)}", ) ]
• mcp_simple_tool/server.py:110-117 (registration)

  Dispatch logic in the @app.call_tool() handler that routes calls to 'get_epss_score' by validating arguments and invoking the tool function.
  elif name == "get_epss_score": if "cve_id" not in arguments: return [ types.TextContent( type="text", text="Error: Missing required argument 'cve_id'" ) ] return await get_epss_score(arguments["cve_id"])
• mcp_simple_tool/server.py:195-208 (registration)

  Tool registration in @app.list_tools() including name, description, and input schema definition for 'get_epss_score'.
  types.Tool( name="get_epss_score", description="Get EPSS exploitability prediction score for a CVE", inputSchema={ "type": "object", "required": ["cve_id"], "properties": { "cve_id": { "type": "string", "description": epss_description, } }, }, ),
• mcp_simple_tool/server.py:198-207 (schema)

  Input schema definition specifying required 'cve_id' string parameter with description.
  inputSchema={ "type": "object", "required": ["cve_id"], "properties": { "cve_id": { "type": "string", "description": epss_description, } }, },
• mcp_simple_tool/tools/epss_lookup.py:9-9 (registration)

  Re-export of the get_epss_score function in tools package __init__ for easy imports.
  import json