binary-re:dynamic-analysis

Dynamic Analysis (Phase 4)

Purpose

Observe actual runtime behavior. Verify hypotheses from static analysis. Capture data that's only visible during execution.

Human-in-the-Loop Requirement

CRITICAL: All execution requires human approval.

Before running ANY binary:

1. Confirm sandbox configuration is acceptable
2. Verify network isolation if required
3. Document what execution will attempt
4. Get explicit approval

Platform Support Matrix

Host Platform	Target Arch	Method	Complexity
Linux x86_64	ARM32/64, MIPS	Native qemu-user	Low
Linux x86_64	x86-32	Native or linux32	Low
macOS (any)	ARM32/64	Docker + binfmt	Medium
macOS (any)	x86-32	Docker --platform linux/i386	Medium
Windows	Any	WSL2 → Linux method	Medium

macOS Docker Setup (One-Time)

# Start Docker runtime (Colima, Docker Desktop, etc.)
colima start

# Register ARM emulation handlers (requires privileged mode)
docker run --rm --privileged --platform linux/arm64 \
  tonistiigi/binfmt --install arm

Docker Mount Best Practices

CRITICAL: On Colima, /tmp mounts often fail silently. Always use home directory paths:

# ✅ GOOD - use home directory
docker run -v ~/code/samples:/work:ro ...

# ❌ BAD - /tmp mounts can fail on Colima
docker run -v /tmp/samples:/work:ro ...

---

Analysis Options

Method	Isolation	Granularity	Best For
QEMU -strace	High	Syscall level	Initial behavior mapping
QEMU + GDB	High	Instruction level	Detailed debugging
Docker	High	Process level	Cross-arch on macOS
Frida	Medium	Function level	Hooking without recompilation
On-device	Low	Full system	When emulation fails

Option A: QEMU User-Mode with Syscall Trace

Safest approach - runs in isolation with syscall logging.

Setup

# Verify sysroot exists
ls /usr/arm-linux-gnueabihf/lib/libc.so*

# ARM 32-bit execution
qemu-arm -L /usr/arm-linux-gnueabihf -strace -- ./binary

# ARM 64-bit execution
qemu-aarch64 -L /usr/aarch64-linux-gnu -strace -- ./binary

Sysroot Selection

Binary ABI	Sysroot Path	QEMU Flag
ARM glibc hard-float	/usr/arm-linux-gnueabihf	-L
ARM glibc soft-float	/usr/arm-linux-gnueabi	-L
ARM64 glibc	/usr/aarch64-linux-gnu	-L
ARM musl	Custom extraction needed	-L

Environment Control

# Set environment variables
qemu-arm -L /sysroot \
  -E HOME=/tmp \
  -E USER=nobody \
  -E LD_DEBUG=bindings \
  -- ./binary

# Unset dangerous variables
qemu-arm -L /sysroot \
  -U LD_PRELOAD \
  -- ./binary

Syscall Analysis

Strace output patterns to watch:

# Network activity
openat.*socket
connect(.*AF_INET
sendto\|send\|write.*socket
recvfrom\|recv\|read.*socket

# File access
openat.*O_RDONLY.*"/etc
openat.*O_WRONLY
stat\|lstat.*"/

# Process operations
execve
fork\|clone

Option B: QEMU + GDB for Deep Debugging

Attach debugger for instruction-level control.

Launch Binary Under GDB

# Start QEMU with GDB server
qemu-arm -g 1234 -L /usr/arm-linux-gnueabihf ./binary &

# Connect with gdb-multiarch
gdb-multiarch -q \
  -ex "set architecture arm" \
  -ex "target remote :1234" \
  -ex "source ~/.gdbinit-gef.py" \
  ./binary

GDB Commands for RE

# Breakpoints
break *0x8400              # Address
break main                 # Symbol
break *0x8400 if $r0 == 5  # Conditional

# Execution control
continue                   # Run until break
stepi                      # Single instruction
nexti                      # Step over calls
finish                     # Run until return

# Inspection
info registers             # All registers
x/20i $pc                  # Disassemble from PC
x/10wx $sp                 # Stack contents
x/s 0x12345                # String at address

# Memory
find 0x8000, 0x10000, "pattern"  # Search memory
dump memory /tmp/mem.bin 0x8000 0x9000  # Extract region

GEF Enhancements

With GEF loaded, additional commands:

gef> vmmap                 # Memory layout
gef> checksec              # Security features
gef> context               # Full state display
gef> hexdump qword $sp 10  # Better hex dump
gef> pcustom               # Structure definitions

Batch Debugging Script

# Create GDB script
cat > analyze.gdb << 'EOF'
set architecture arm
target remote :1234
break main
continue
info registers
x/20i $pc
continue
quit
EOF

# Run batch
gdb-multiarch -batch -x analyze.gdb ./binary

Option C: Frida for Function Hooking

Intercept function calls without modifying binary.

⚠️ Architecture Constraint: Frida requires native-arch execution. It cannot attach to QEMU-user targets.

Scenario	Works?	Alternative
Native binary (x86_64 on x86_64)	✅	-
Cross-arch under QEMU-user	❌	Use on-device frida-server
Docker native-arch container	✅	-
Docker cross-arch (emulated)	❌	Use on-device frida-server

For cross-arch Frida, deploy frida-server to the target device:

# On target device:
./frida-server &

# On host:
frida -H device:27042 -f ./binary -l hook.js --no-pause

Basic Hook

// hook_connect.js
Interceptor.attach(Module.findExportByName(null, "connect"), {
  onEnter: function(args) {
    console.log("[connect] Called");
    var sockaddr = args[1];
    var family = sockaddr.readU16();
    if (family == 2) { // AF_INET
      var port = sockaddr.add(2).readU16();
      var ip = sockaddr.add(4).readByteArray(4);
      console.log("  Port: " + ((port >> 8) | ((port & 0xff) << 8)));
      console.log("  IP: " + new Uint8Array(ip).join("."));
    }
  },
  onLeave: function(retval) {
    console.log("  Return: " + retval);
  }
});

# Run with Frida
frida -f ./binary -l hook_connect.js --no-pause

Tracing All Calls to Library

// trace_libcurl.js
var libcurl = Process.findModuleByName("libcurl.so.4");
if (libcurl) {
  libcurl.enumerateExports().forEach(function(exp) {
    if (exp.type === "function") {
      Interceptor.attach(exp.address, {
        onEnter: function(args) {
          console.log("[" + exp.name + "] called");
        }
      });
    }
  });
}

Memory Inspection

// dump_memory.js
var base = Module.findBaseAddress("binary");
console.log("Base: " + base);

// Dump region
var data = base.add(0x1000).readByteArray(256);
console.log(hexdump(data, { offset: 0, length: 256 }));

Option D: Docker-Based Cross-Architecture (macOS)

Use Docker for cross-arch execution when native QEMU unavailable.

ARM32 Binary on macOS

docker run --rm --platform linux/arm/v7 \
  -v ~/code/samples:/work:ro \
  arm32v7/debian:bullseye-slim \
  sh -c '
    # Fix linker path mismatch (common issue)
    ln -sf /lib/ld-linux-armhf.so.3 /lib/ld-linux.so.3 2>/dev/null || true

    # Install dependencies if needed (check rabin2 -l output)
    apt-get update -qq && apt-get install -qq -y libcap2 libacl1 2>/dev/null

    # Run with library debug output (strace alternative)
    LD_DEBUG=libs /work/binary args
  '

ARM64 Binary on macOS

docker run --rm --platform linux/arm64 \
  -v ~/code/samples:/work:ro \
  arm64v8/debian:bullseye-slim \
  sh -c 'LD_DEBUG=libs /work/binary args'

x86 32-bit Binary on macOS

docker run --rm --platform linux/i386 \
  -v ~/code/samples:/work:ro \
  i386/debian:bullseye-slim \
  sh -c '/work/binary args'

Tracing Limitations in Docker/QEMU User-Mode

Method	Works?	Alternative
strace	❌ (ptrace not implemented)	LD_DEBUG=files,libs
ltrace	❌ (same reason)	Direct observation or Frida
gdb	✓ (with QEMU -g flag)	N/A

LD_DEBUG Options (strace alternative)

LD_DEBUG=libs     # Library search and loading
LD_DEBUG=files    # File operations during loading
LD_DEBUG=symbols  # Symbol resolution
LD_DEBUG=bindings # Symbol binding details
LD_DEBUG=all      # Everything (verbose)

---

Option E: On-Device Analysis

When emulation fails or device-specific behavior needed.

Remote GDB via gdbserver

# On target device (via SSH/ADB)
gdbserver :1234 ./binary

# On host (with port forward)
ssh -L 1234:localhost:1234 user@device &
gdb-multiarch -q \
  -ex "target remote localhost:1234" \
  ./binary

Remote strace (if available)

# On target device
strace -f -o /tmp/trace.log ./binary

# Pull log
scp user@device:/tmp/trace.log .

Sandbox Configuration

Minimal Sandbox (nsjail)

nsjail \
  --mode o \
  --chroot /sysroot \
  --user 65534 \
  --group 65534 \
  --disable_clone_newnet \
  --rlimit_as 512 \
  --time_limit 60 \
  -- /binary

QEMU with Resource Limits

# CPU time limit
timeout 60 qemu-arm -L /sysroot -strace ./binary

# Memory limit via cgroup (requires setup)
cgexec -g memory:qemu_sandbox qemu-arm -L /sysroot ./binary

Anti-Analysis Detection

Before dynamic analysis, check for common anti-debugging/anti-analysis patterns:

Static Detection (Pre-Execution)

# Check for anti-debug strings/imports
strings -a binary | grep -Ei 'ptrace|anti|debugger|seccomp|LD_PRELOAD|/proc/self'

# r2: Look for ptrace/prctl/seccomp imports
r2 -q -c 'iij' binary | jq '.[].name' | grep -Ei 'ptrace|prctl|seccomp'

# Common anti-analysis indicators:
# - ptrace(PTRACE_TRACEME) - Prevent debugger attach
# - prctl(PR_SET_DUMPABLE, 0) - Prevent core dumps
# - seccomp - Syscall filtering
# - /proc/self/status checks - Detect TracerPid

Runtime Detection

# If native execution possible:
strace -f ./binary 2>&1 | grep -E 'ptrace|prctl|seccomp|/proc/self'

Mitigation Strategies

Pattern	Detection	Bypass
ptrace(TRACEME)	Returns EPERM if debugger attached	Patch call to NOP, use QEMU
/proc/self/status check	Reads TracerPid field	Use QEMU (no /proc emulation)
Timing checks	gettimeofday/rdtsc loops	Single-step with GDB, patch checks
Self-checksum	Reads own binary/memory	Compute expected checksum, patch

When anti-analysis detected: Prefer QEMU-strace over GDB (fewer detection vectors), or patch checks in r2 before execution.

---

Error Recovery

Error	Cause	Solution
Unsupported syscall	QEMU limitation	Try Qiling or on-device
Invalid ELF image	Wrong arch/sysroot	Verify file output
Segfault at 0x0	Missing library	Check ldd equivalent
QEMU hangs	Blocking on I/O	Add timeout, check strace
Anti-debugging	Detection code	Use Frida stalker mode
exec format error in Docker	binfmt not registered	Run tonistiigi/binfmt --install arm
ld-linux.so.3 not found	Linker path mismatch	Create symlink in container
libXXX.so not found	Missing dependency	apt install in container
Empty mount in Docker	Colima /tmp issue	Use ~/ path instead of /tmp/
ptrace: Operation not permitted	strace in QEMU	Use LD_DEBUG instead

Output Format

Record observations as structured data:

{
  "experiment": {
    "id": "exp_001",
    "method": "qemu_strace",
    "command": "qemu-arm -L /usr/arm-linux-gnueabihf -strace ./binary",
    "duration_secs": 12,
    "exit_code": 0
  },
  "syscall_summary": {
    "network": {
      "socket": 2,
      "connect": 1,
      "send": 5,
      "recv": 3
    },
    "file": {
      "openat": 4,
      "read": 12,
      "close": 4
    }
  },
  "network_connections": [
    {
      "family": "AF_INET",
      "address": "192.168.1.100",
      "port": 8443,
      "protocol": "tcp"
    }
  ],
  "files_accessed": [
    {"path": "/etc/config.json", "mode": "read"},
    {"path": "/var/log/app.log", "mode": "write"}
  ],
  "hypotheses_tested": [
    {
      "hypothesis_id": "hyp_001",
      "result": "confirmed",
      "evidence": "connect() to 192.168.1.100:8443 observed"
    }
  ]
}

Knowledge Journaling

After dynamic analysis, record findings for episodic memory:

[BINARY-RE:dynamic] {filename} (sha256: {hash})

Execution method: {qemu-strace|qemu-gdb|frida|on-device}
DECISION: Approved execution with {sandbox_config} (rationale: {why_safe})

Runtime observations:
  FACT: Binary reads {path} (source: strace openat)
  FACT: Binary connects to {ip}:{port} (source: strace connect)
  FACT: Binary writes to {path} (source: strace write)
  FACT: Function {addr} receives args {values} at runtime (source: gdb)

Syscall summary:
  Network: {socket|connect|send|recv counts}
  File: {open|read|write|close counts}
  Process: {fork|exec|clone counts}

HYPOTHESIS UPDATE: {confirmed or refined theory} (confidence: {new_value})
  Confirmed by: {runtime observation}
  Contradicted by: {if any}

New questions:
  QUESTION: {runtime-discovered unknown}

Answered questions:
  RESOLVED: {question} → {runtime evidence}

Example Journal Entry

[BINARY-RE:dynamic] thermostat_daemon (sha256: a1b2c3d4...)

Execution method: qemu-strace
DECISION: Approved execution with network-blocked sandbox (rationale: static analysis shows outbound only, no server)

Runtime observations:
  FACT: Binary reads /etc/thermostat.conf at startup (source: strace openat)
  FACT: Binary attempts connect to 93.184.216.34:443 (source: strace connect)
  FACT: Binary writes to /var/log/thermostat.log (source: strace openat O_WRONLY)
  FACT: sleep(30) called between network attempts (source: strace nanosleep)

Syscall summary:
  Network: socket(2), connect(1-blocked), send(0), recv(0)
  File: openat(4), read(12), write(8), close(4)
  Process: none

HYPOTHESIS UPDATE: Telemetry client confirmed - reads config, attempts HTTPS to thermco servers every 30s (confidence: 0.95)
  Confirmed by: connect() to expected IP, sleep(30) timing, config file read
  Contradicted by: none

Answered questions:
  RESOLVED: "Does it actually phone home?" → Yes, connect() to 93.184.216.34:443 observed
  RESOLVED: "What files does it access?" → /etc/thermostat.conf (read), /var/log/thermostat.log (write)

Next Steps

→ binary-re-synthesis to compile findings into report → Additional static analysis if new functions identified → Repeat with different inputs if behavior varies