Reverse Engineering (Ghidra + Joern)

Combined reverse engineering skill using Ghidra for binary decompilation and Joern for Code Property Graph analysis.

Workflow

1. Download binary — download_from_remote to fetch target binary from remote server
2. Ghidra analysis — Decompile, list functions, find dangerous calls, trace cross-references
3. Joern CPG analysis — Import into CPG, query vulnerability patterns, trace taint flows
4. Validate findings — Cross-reference Ghidra decompilation with Joern data flow results

Part 1: Ghidra Headless Analysis

Quick Start

# One-shot: import + analyze + run script
analyzeHeadless /tmp/ghidra_proj Project \
    -import <binary> \
    -postScript <script.py> \
    -deleteProject 2>&1

Decompile Functions

from ghidra.app.decompiler import DecompInterface

decomp = DecompInterface()
decomp.openProgram(currentProgram)
fm = currentProgram.getFunctionManager()

# Decompile all (limit 50)
count = 0
for func in fm.getFunctions(True):
    result = decomp.decompileFunction(func, 30, monitor)
    if result.decompileCompleted():
        print(f"=== {func.getName()} @ {func.getEntryPoint()} ===")
        print(result.getDecompiledFunction().getC())
    count += 1
    if count > 50:
        break

# Decompile specific function
target = "<FUNCTION_NAME>"
for func in fm.getFunctions(True):
    if func.getName() == target:
        result = decomp.decompileFunction(func, 60, monitor)
        if result.decompileCompleted():
            print(result.getDecompiledFunction().getC())
        break

Find Dangerous Function Calls

dangerous = ["system", "popen", "execve", "strcpy", "sprintf",
             "gets", "strcat", "scanf", "memcpy", "doSystemCmd"]
fm = currentProgram.getFunctionManager()
for func in fm.getFunctions(True):
    name = func.getName().lower()
    if any(d in name for d in dangerous):
        print(f"\nDANGEROUS: {func.getName()} @ {func.getEntryPoint()}")
        for ref in getReferencesTo(func.getEntryPoint()):
            caller = fm.getFunctionContaining(ref.getFromAddress())
            if caller:
                print(f"  Called from: {caller.getName()} @ {ref.getFromAddress()}")

String Cross-References

import re
pattern = "<SEARCH_PATTERN>"  # e.g., "password|admin|system"
listing = currentProgram.getListing()
fm = currentProgram.getFunctionManager()
for data in listing.getDefinedData(True):
    if data.hasStringValue():
        val = str(data.getValue())
        if re.search(pattern, val, re.IGNORECASE):
            addr = data.getAddress()
            print(f"\nSTRING: '{val}' @ {addr}")
            for ref in getReferencesTo(addr):
                func = fm.getFunctionContaining(ref.getFromAddress())
                if func:
                    print(f"  Referenced by: {func.getName()} @ {ref.getFromAddress()}")

Ghidra Tips

• Large binaries: Use -analysisTimeoutPerFile flag (default 300s)
• Wrong arch detection: Use -processor flag (e.g., -processor ARM:LE:32:v7)
• Stripped binaries: Ghidra auto-creates function entries, names will be FUN_xxxxx

Part 2: Joern CPG Analysis

Quick Start

# Import C source directory into CPG
joern-parse /path/to/source --output /tmp/firmware.cpg

# Launch Joern and load CPG
joern
importCpg("/tmp/firmware.cpg")

Dangerous Function Calls

// Find all calls to dangerous functions
cpg.call.name("system|popen|execve|exec|strcpy|strcat|sprintf|gets|scanf|sscanf|vsprintf").l

// Find strcpy with non-constant source
cpg.call.name("strcpy").argument(2).whereNot(_.isLiteral).l

Taint Analysis (Source → Sink)

// Define sources: user-controllable input
val sources = cpg.call.name("recv|read|fread|fgets|getenv|scanf|recvfrom").argument(1)

// Define sinks: dangerous execution
val sinks = cpg.call.name("system|popen|execve|exec").argument(1)

// Find taint flows
sinks.reachableByFlows(sources).p

Command Injection Patterns

val userInput = cpg.call.name("recv|read|getenv|fgets").argument(1)
val cmdExec = cpg.call.name("system|popen|execve").argument(1)
cmdExec.reachableByFlows(userInput).p

Buffer Overflow Patterns

cpg.call.name("strcpy|strcat|gets|sprintf")
  .where(_.argument(1).isIdentifier)
  .l

Authentication & Hardcoded Credentials

cpg.call.name("strcmp|strncmp")
  .where(_.argument.isLiteral)
  .l

Non-Interactive Batch Mode

joern --script /path/to/query.sc --params cpgFile=/tmp/firmware.cpg

Joern Tips

• Binary CPG limitations: Binary-level CPG has less precise type info than source CPG
• Large codebases: Use --max-num-def to limit analysis scope
• Joern memory: Set JAVA_OPTS="-Xmx4g" for large firmware images

References

• Ghidra script templates: See references/ghidra-scripts.md for vulnerability scanner, call graph tracer, NVRAM tracker
• CPG query cookbook: See references/cpg-queries.md for IoT-specific query patterns
• Batch scan script: Run scripts/joern_batch_scan.py to scan extracted filesystem for vulnerable binaries