How Hook Detection Works

Hook detection mechanisms can differ between Android and iOS due to the differences in their operating systems. Below, we break down how hook detection typically works on each platform.

For Android

On Android, hooking often relies on tools that inject code into apps or modify the Android runtime (often requiring root access). Thus, Android apps employ a variety of methods to detect such interference:

Checking for Hooking Frameworks: The app can programmatically look for signs of popular hooking frameworks like Frida or Xposed. For instance, it might scan running processes and loaded libraries for names associated with Frida (such as a process listening on Frida’s default port, or the presence of libfrida libraries in memory). Similarly, it might try to detect Xposed by searching for known Xposed classes (like de.robv.android.xposed.XposedBridge) or files that the Xposed framework leaves on the system. If any of these indicators are found, the app concludes a hook might be present.
Runtime Integrity Checks: The app can perform self-checks on its code at runtime. This could involve verifying checksums or hashes of critical code segments to ensure they haven’t been modified in memory. If a hooking tool has patched or overwritten some instructions (as hooks often do), these integrity checks might catch the unexpected changes
Anti-Debugging Measures: Many hooking tools use debugging techniques under the hood (they attach to the app process similarly to how a debugger would). To counter this, apps implement anti-debugging. Techniques include detecting if the process is being debugged (using system calls like ptrace on Android), or if suspicious system flags are set that indicate an attachment. If the app notices it’s under a debugger or instrumentation when it shouldn’t be, it can assume a hooking attempt (since Frida often uses a JDWP debugger or ptrace mechanism). Some apps even deliberately perform slight “delays” or check execution timing, since a hooked environment may respond slightly slower due to the instrumentation.
Environment and Device Checks: A lot of hooking on Android requires root access. So apps often integrate root detection as part of hook detection. They check for root indicators (presence of su binary, known root app packages, modified system paths). Additionally, they check if the app is running in unusual environments: for example, inside an emulator or a virtual space (there are tools that allow hooking without root by running the app in a modified virtual environment). If the app detects it’s in an emulator or sees signs of frameworks like VirtualXposed (which allows Xposed modules without root), it can raise a red flag. Google’s SafetyNet/Play Integrity API results can also inform this – if the device fails integrity checks, the app may suspect that hooking tools could be active and be extra vigilant.
Monitoring System Calls and APIs: Advanced implementations may monitor certain sensitive API calls that hooking tools use. For example, on Android, a hooking tool might use the ptrace system call to attach to the app, or it may call functions to load custom libraries. An app can attempt to detect if those actions occur during its runtime. While an app can’t easily block these low-level calls (without OS support), noticing them can be a sign of intrusion.

Once any of these methods detects something fishy, the app can take action. Common responses on Android include: immediately closing the app (to prevent further tampering), logging the event (for analytics or forensic purposes), or disabling sensitive features (e.g. not allowing login or transactions if hooking is detected). Some security-conscious apps display a warning like “Untrusted environment detected” and exit, which is a direct result of these checks.

For IOS

On iOS, hooking is less common in non-jailbroken devices due to Apple’s strict app sandbox and code signing requirements. However, in jailbroken devices (where a user has removed iOS restrictions), hooking becomes possible using tools like Cydia Substrate or Frida. Therefore, iOS hook detection often starts with jailbreak detection and then goes into deeper checks:

Jailbreak Detection: Since an iOS app normally shouldn’t be able to have new code injected at runtime (unless the device is jailbroken), the first step is checking if the device is compromised. The app checks for signs like the existence of Cydia (the jailbreak app store), the ability to write to areas of the filesystem that should be protected, or the presence of known jailbreak files and processes. If the device is jailbroken, the app assumes the security model is broken and hooking is possible, and may choose to not run or run in a restricted mode.
Detecting Injected Libraries: iOS hooking frameworks (like Substrate or Frida’s Gadget) work by injecting dynamic libraries (dylibs) into apps. An app can programmatically list the dynamic libraries loaded in its process (using APIs like dyld functions). If it finds a library that is not part of iOS or the app itself, that’s a big warning sign. For example, if something like FridaGadget.dylib or any library residing in ‘ /Library/MobileSubstrate/ ‘ is loaded, the app is likely hooked. Apps can maintain a list of expected module names and paths, and flag any anomalies.
Function Pointer Verification: iOS developers can perform checks on critical functions to see if they’ve been tampered with. For example, iOS apps might verify that certain Security or Crypto functions are still pointing to Apple’s original implementations. If a hook (via Substrate or the fishhook technique) has rerouted those functions to attacker code, the addresses or hashes won’t match the known good values. This is a more technical method, but it can catch cases where an attacker patches functions in memory. Essentially, the app knows what the start of a function is supposed to look like; if it’s been overwritten with a jump to elsewhere, that indicates a hook.
Anti-Debug and Anti-Attach: Just as on Android, on iOS an app can detect debugging attempts. iOS provides APIs to check if the process is being debugged (like checking the AMFID and other process flags). Also, iOS apps can use the ptrace call with the PT_DENY_ATTACH option to proactively prevent debuggers (which also blocks some hooking techniques that rely on debugger attachment). If an attacker cannot attach a debugger or instrument easily, it thwarts many hooking attempts. Some apps repeatedly check for any new process that tries to attach and immediately kill the app if detected.
Timing and Behavior Checks: This is less common on iOS due to the performance overhead, but conceptually an app could perform operations that should be quick and see if there’s an unusual delay or behavior (which might happen if a hook is intercepting calls). Also, the app might check if certain system calls return expected values; if a hook is faking responses (like returning false for “Is this device jailbroken?” when it actually is), a clever app might cross-verify via multiple methods to catch the lie.

In practice, iOS relies heavily on the assumption that if the device isn’t jailbroken, hooking is nearly impossible. So many iOS apps simply don’t worry about hooking beyond jailbreak detection. But for high-security apps that must even consider malicious insiders with jailbroken devices, the above measures add extra layers of defense. If a hook is detected, iOS apps often react similarly to Android ones: shut down or disable functionality. For instance, some banking apps on iOS will instantly close if they sense any jailbreak/hook to protect the user’s account.

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Last updated 16 days ago

For Android

Checking for Hooking Frameworks: The app can programmatically look for signs of popular hooking frameworks like Frida or Xposed. For instance, it might scan running processes and loaded libraries for names associated with Frida (such as a process listening on Frida’s default port, or the presence of libfrida libraries in memory). Similarly, it might try to detect Xposed by searching for known Xposed classes (like de.robv.android.xposed.XposedBridge) or files that the Xposed framework leaves on the system. If any of these indicators are found, the app concludes a hook might be present.

Runtime Integrity Checks: The app can perform self-checks on its code at runtime. This could involve verifying checksums or hashes of critical code segments to ensure they haven’t been modified in memory. If a hooking tool has patched or overwritten some instructions (as hooks often do), these integrity checks might catch the unexpected changes

Anti-Debugging Measures: Many hooking tools use debugging techniques under the hood (they attach to the app process similarly to how a debugger would). To counter this, apps implement anti-debugging. Techniques include detecting if the process is being debugged (using system calls like ptrace on Android), or if suspicious system flags are set that indicate an attachment. If the app notices it’s under a debugger or instrumentation when it shouldn’t be, it can assume a hooking attempt (since Frida often uses a JDWP debugger or ptrace mechanism). Some apps even deliberately perform slight “delays” or check execution timing, since a hooked environment may respond slightly slower due to the instrumentation.

Environment and Device Checks: A lot of hooking on Android requires root access. So apps often integrate root detection as part of hook detection. They check for root indicators (presence of su binary, known root app packages, modified system paths). Additionally, they check if the app is running in unusual environments: for example, inside an emulator or a virtual space (there are tools that allow hooking without root by running the app in a modified virtual environment). If the app detects it’s in an emulator or sees signs of frameworks like VirtualXposed (which allows Xposed modules without root), it can raise a red flag. Google’s SafetyNet/Play Integrity API results can also inform this – if the device fails integrity checks, the app may suspect that hooking tools could be active and be extra vigilant.

Monitoring System Calls and APIs: Advanced implementations may monitor certain sensitive API calls that hooking tools use. For example, on Android, a hooking tool might use the ptrace system call to attach to the app, or it may call functions to load custom libraries. An app can attempt to detect if those actions occur during its runtime. While an app can’t easily block these low-level calls (without OS support), noticing them can be a sign of intrusion.

For IOS

Jailbreak Detection: Since an iOS app normally shouldn’t be able to have new code injected at runtime (unless the device is jailbroken), the first step is checking if the device is compromised. The app checks for signs like the existence of Cydia (the jailbreak app store), the ability to write to areas of the filesystem that should be protected, or the presence of known jailbreak files and processes. If the device is jailbroken, the app assumes the security model is broken and hooking is possible, and may choose to not run or run in a restricted mode.

Detecting Injected Libraries: iOS hooking frameworks (like Substrate or Frida’s Gadget) work by injecting dynamic libraries (dylibs) into apps. An app can programmatically list the dynamic libraries loaded in its process (using APIs like dyld functions). If it finds a library that is not part of iOS or the app itself, that’s a big warning sign. For example, if something like FridaGadget.dylib or any library residing in ‘ /Library/MobileSubstrate/ ‘ is loaded, the app is likely hooked. Apps can maintain a list of expected module names and paths, and flag any anomalies.

Function Pointer Verification: iOS developers can perform checks on critical functions to see if they’ve been tampered with. For example, iOS apps might verify that certain Security or Crypto functions are still pointing to Apple’s original implementations. If a hook (via Substrate or the fishhook technique) has rerouted those functions to attacker code, the addresses or hashes won’t match the known good values. This is a more technical method, but it can catch cases where an attacker patches functions in memory. Essentially, the app knows what the start of a function is supposed to look like; if it’s been overwritten with a jump to elsewhere, that indicates a hook.

Anti-Debug and Anti-Attach: Just as on Android, on iOS an app can detect debugging attempts. iOS provides APIs to check if the process is being debugged (like checking the AMFID and other process flags). Also, iOS apps can use the ptrace call with the PT_DENY_ATTACH option to proactively prevent debuggers (which also blocks some hooking techniques that rely on debugger attachment). If an attacker cannot attach a debugger or instrument easily, it thwarts many hooking attempts. Some apps repeatedly check for any new process that tries to attach and immediately kill the app if detected.

Timing and Behavior Checks: This is less common on iOS due to the performance overhead, but conceptually an app could perform operations that should be quick and see if there’s an unusual delay or behavior (which might happen if a hook is intercepting calls). Also, the app might check if certain system calls return expected values; if a hook is faking responses (like returning false for “Is this device jailbroken?” when it actually is), a clever app might cross-verify via multiple methods to catch the lie.