CPG Analysis Skill Skill

CPG Analysis Skill

Purpose: Deep code analysis beyond AST. Use Joern for full Code Property Graph (control flow, data flow, program dependencies) and CodeQL for interprocedural taint analysis and vulnerability detection.

These are opt-in tools. They require Docker/JVM (Joern) or CodeQL CLI. Use codebase-memory-mcp (Tier 1, always-on) for everyday navigation. Use these for deep analysis when Tier 1 is not enough.

┌────────────────────────────────────────────────────────────────┐
│  CODE PROPERTY GRAPH = AST + CFG + CDG + DDG + PDG             │
│  ─────────────────────────────────────────────────────────────│
│  AST  = Abstract Syntax Tree (structure)                       │
│  CFG  = Control Flow Graph (execution paths)                   │
│  CDG  = Control Dependency Graph (conditional dependencies)    │
│  DDG  = Data Dependency Graph (data flow between statements)   │
│  PDG  = Program Dependency Graph (CDG + DDG combined)          │
│                                                                │
│  Tier 2 (Joern): Full CPG with 40+ query tools                │
│  Tier 3 (CodeQL): Interprocedural taint + security queries     │
└────────────────────────────────────────────────────────────────┘

Tier Selection Guide

Simple symbol lookup, dependency trace, blast radius?
  → Tier 1: codebase-memory-mcp (always on, sub-ms)

Control flow paths, data flow, dead code, complex refactoring?
  → Tier 2: Joern CPG (on-demand, seconds)

Security audit, taint analysis, vulnerability detection?
  → Tier 3: CodeQL (on-demand, seconds to minutes)

Full security review before release?
  → All three tiers in sequence

Tier 2: Joern CPG (CodeBadger MCP)

When to Use Joern

| Scenario | Why Joern | Tier 1 Can't Do This | |----------|-----------|---------------------| | Trace data flow through functions | Full DDG traversal | Tier 1 has no data flow | | Understanding control flow paths | CFG analysis with branch conditions | Tier 1 has no CFG | | Finding dead/unreachable code | PDG reachability analysis | Tier 1 only detects unused exports | | Complex refactoring impact | Cross-function dependency chains | Tier 1 limited to call graph | | Auditing third-party library usage | Deep call chain traversal | Tier 1 stops at import boundary | | Understanding exception flow | CFG includes throw/catch paths | Tier 1 ignores exceptions |

Key MCP Tools (Joern/CodeBadger)

| Tool | Purpose | Example Query | |------|---------|---------------| | generate_cpg | Build CPG for project | First-time setup or after major changes | | get_cpg_status | Check CPG build status | Verify CPG is ready before querying | | run_cpgql_query | Run arbitrary CPGQL queries | cpg.method("login").callOut.code.l | | get_cpgql_syntax_help | Query language reference | When unsure about query syntax | | get_cfg | Control flow graph for a method | Understand execution paths in a function | | list_methods | List all methods in project | Overview of available functions | | get_method_source | Get source code of a method | Read specific function source | | list_calls | List calls from/to a method | Caller/callee analysis | | get_call_graph | Full call graph visualization | Understand call chains | | get_type_definition | Type/class definitions | Understand type hierarchy |

Supported Languages (Joern)

Java, Scala, C/C++, Python, JavaScript, TypeScript, PHP, Ruby, Go, Kotlin, Swift, Lua

Not supported: Rust (use CodeQL for Rust)

MCP Configuration (Joern)

{
  "mcpServers": {
    "codebadger": {
      "url": "http://localhost:4242/mcp",
      "type": "http"
    }
  }
}

Prerequisites

Docker (for Joern backend)
Python 3.10+ (for MCP server)
Install: ~/.claude/install-graph-tools.sh --joern

Common CPGQL Queries

// Find all methods that handle user input
cpg.method.where(_.parameter.name(".*input.*|.*request.*")).name.l

// Trace data flow from parameter to return
cpg.method("processPayment").parameter.reachableBy(cpg.method("processPayment").methodReturn).l

// Find methods with high cyclomatic complexity
cpg.method.where(_.controlStructure.size > 10).name.l

// Dead code: methods with no callers
cpg.method.where(_.callIn.size == 0).filter(_.name != "main").name.l

// Exception flow: methods that can throw but callers don't catch
cpg.method.where(_.ast.isThrow.size > 0).callIn.method.filter(_.ast.isTry.size == 0).name.l

Tier 3: CodeQL

When to Use CodeQL

| Scenario | Why CodeQL | Other Tiers Can't Do This | |----------|-----------|--------------------------| | Security audit before release | Interprocedural taint analysis | Joern has basic taint, CodeQL is deeper | | Reviewing auth/payment code | Data flow from source to sink | Cross-function, cross-file taint | | PR security review | Targeted vulnerability scan | Pre-built OWASP query packs | | Compliance checking | CWE/OWASP pattern matching | Curated security query suites | | Rust security analysis | Full Rust support | Joern doesn't support Rust |

Key MCP Tools (CodeQL)

| Tool | Purpose | |------|---------| | run_query | Execute a CodeQL query against the database | | find_definitions | Locate symbol definitions | | find_references | Find all references to a symbol | | get_results | Parse BQRS (Binary Query Result Sets) |

Supported Languages (CodeQL)

C/C++, C#, Go, Java, Kotlin, JavaScript, TypeScript, Python, Ruby, Swift, Rust

MCP Configuration (CodeQL)

{
  "mcpServers": {
    "codeql": {
      "command": "codeql-mcp",
      "args": ["--database", ".code-graph/codeql-db"]
    }
  }
}

Prerequisites

CodeQL CLI (brew install codeql on macOS)
Install: ~/.claude/install-graph-tools.sh --codeql

Common CodeQL Patterns

// SQL injection: user input flows to SQL query
import python
from DataFlow::PathNode source, DataFlow::PathNode sink
where TaintTracking::hasFlowPath(source, sink)
  and source instanceof RemoteFlowSource
  and sink instanceof SqlExecution
select sink, source, sink, "SQL injection from $@.", source, "user input"

// Unvalidated redirect
from DataFlow::PathNode source, DataFlow::PathNode sink
where source instanceof RemoteFlowSource
  and sink instanceof RedirectSink
select sink, "Unvalidated redirect from user input"

Combined Workflow: Deep Analysis

When performing security review or complex refactoring, use all tiers:

1. SCOPE       → Tier 1: detect_changes / get_architecture
                 Identify files and modules in scope

2. STRUCTURE   → Tier 1: search_graph / trace_call_path
                 Map the call graph and dependencies

3. FLOW        → Tier 2: get_cfg / run_cpgql_query
                 Analyze control flow and data flow paths

4. SECURITY    → Tier 3: run_query with taint analysis
                 Check for vulnerabilities in data paths

5. REPORT      → Combine findings from all tiers
                 Prioritize: Critical > High > Medium > Low

Anti-Patterns

| Anti-Pattern | Do This Instead | |-------------|-----------------| | Using Joern/CodeQL for simple symbol lookup | Use Tier 1 search_graph (sub-ms vs seconds) | | Running full CPG build on every commit | Build CPG on-demand; use Tier 1 for continuous monitoring | | Querying Joern without checking get_cpg_status | Always verify CPG is built and current before querying | | Running CodeQL without a specific security question | Have a hypothesis first; CodeQL queries are expensive | | Ignoring Tier 1 blast radius before deep analysis | Always scope with Tier 1 first, then go deep on flagged areas | | Using CodeQL for non-security structural queries | Use Joern CPGQL for structural/flow queries; CodeQL for security |

Agent Skills: CPG Analysis Skill

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