Android Services 101

src/mobile-pentesting/android-app-pentesting/android-applications-basics.md

@@ -395,6 +395,112 @@ if (dpm.isAdminActive(adminComponent)) {
 }
 ```
 
+
+## Enumerating and Exploiting AIDL / Binder Services
+
+Android *Binder* IPC exposes many **system and vendor-provided services**. Those services become an **attack surface** when they are exported without a proper permission check (the AIDL layer itself performs *no* access-control).
+
+### 1. Discover running services
+
+```bash
+# from an adb shell (USB or wireless)
+service list               # simple one-liner
+am list services           # identical output, ActivityManager wrapper
+```
+
+Output is a numbered list such as:
+```
+145  mtkconnmetrics: [com.mediatek.net.connectivity.IMtkIpConnectivityMetrics]
+146  wifi             : [android.net.wifi.IWifiManager]
+```
+* The **index** (first column) is assigned at runtime – do ***not*** rely on it across reboots.
+* The **Binder name** (e.g. `mtkconnmetrics`) is what will be passed to `service call`.
+* The value inside the brackets is the fully-qualified **AIDL interface** that the stub was generated from.
+
+### 2. Obtain the interface descriptor (PING)
+Every Binder stub automatically implements **transaction code `0x5f4e5446`** (`1598968902` decimal, ASCII "_NTF").
+
+```bash
+# "ping" the service
+service call mtkconnmetrics 1    # 1 == decimal 1598968902 mod 2^32
+```
+A valid reply returns the interface name encoded as a UTF-16 string inside a `Parcel`.
+
+### 3. Calling a transaction
+Syntax: `service call <name> <code> [type value ...]`
+
+Common argument specifiers:
+* `i32 <int>` – signed 32-bit value
+* `i64 <long>` – signed 64-bit  value
+* `s16 <string>` – UTF-16 string (Android 13+ uses `utf16`)
+
+Example – start network monitoring with uid **1** on a MediaTek handset:
+```bash
+service call mtkconnmetrics 8 i32 1
+```
+
+### 4. Brute-forcing unknown methods
+When header files are unavailable you can **iterate the code** until the error changes from:
+```
+Result: Parcel(00000000 00000000)  # "Not a data message"
+```
+to a normal `Parcel` response or `SecurityException`.
+
+```bash
+for i in $(seq 1 50); do
+    printf "[+] %2d -> " $i
+    service call mtkconnmetrics $i 2>/dev/null | head -1
+done
+```
+
+If the service was compiled **with proguard** the mapping must be guessed – see next step.
+
+### 5. Mapping codes ↔ methods via onTransact()
+Decompile the jar/odex that implements the interface (for AOSP stubs check `/system/framework`; OEMs often use `/system_ext` or `/vendor`).  
+Search for `Stub.onTransact()` – it contains a giant `switch(transactionCode)`:
+
+```java
+case TRANSACTION_updateCtaAppStatus:      // 5
+    data.enforceInterface(DESCRIPTOR);
+    int appId  = data.readInt();
+    boolean ok = data.readInt() != 0;
+    updateCtaAppStatus(appId, ok);
+    reply.writeNoException();
+    return true;
+```
+
+Now the prototype and **parameter types** are crystal clear.
+
+### 6. Spotting missing permission checks
+The implementation (often an inner `Impl` class) is responsible for authorisation:
+
+```java
+private void updateCtaAppStatus(int uid, boolean status) {
+    if (!isPermissionAllowed()) {
+        throw new SecurityException("uid " + uid + " rejected");
+    }
+    /* privileged code */
+}
+```
+Absence of such logic or a whitelist of privileged UIDs (e.g. `uid == 1000 /*system*/`) is a **vulnerability indicator**.
+
+Case study – *MediaTek* `startMonitorProcessWithUid()` (transaction **8**) fully executes a Netlink message **without** any permission gate, allowing an unprivileged app to interact with the kernel’s Netfilter module and spam the system log.
+
+### 7. Automating the assessment
+Tools / scripts that speed-up Binder reconnaissance:
+* [binderfs](https://android.googlesource.com/platform/frameworks/native/+/master/cmds/binderfs/) – exposes `/dev/binderfs` with per-service nodes
+* [`binder-scanner.py`](https://github.com/adenflare/binder-scanner) – walks the binder table and prints ACLs
+* Frida shortcut: `Java.perform(()=>console.log(android.os.ServiceManager.listServices().toArray()))`
+
+---
+
+## References
+
+- [Android Services 101 – Pentest Partners](https://www.pentestpartners.com/security-blog/android-services-101/)
+- [Android Developer Docs – AIDL](https://developer.android.com/guide/components/aidl)
+- [Android Developer Docs – IBinder](https://developer.android.com/reference/android/os/IBinder)
+- [Understanding Binder, Talk @ Google](https://www.youtube.com/watch?v=O-UHvFjxwZ8)
+
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