android-intent-security

name	android-intent-security
description	Best practices for Android Intent security. Use this skill when auditing component configurations in AndroidManifest.xml activities, services, receivers) or source code handling incoming Intents (getIntent, getParcelableExtra) to prevent Intent Redirection and unauthorized access.
license	Complete terms in LICENSE.txt
metadata	{"author":"Google LLC","last-updated":"2026-06-25","keywords":["recipe","Android","Security","Intent","Redirection","PendingIntent","ContentProvider","Service","Signature","Verification","sanitizer","Vulnerability","Best Practices"]}

This skill provides guidelines and patterns to secure Android components (Activities, Services, Broadcast Receivers, Content Providers) and handle Intents safely, preventing privilege escalation and unauthorized access.

Glossary

• Intent: An asynchronous messaging object used to request an action from another app component.
• Exported component: A component (android:exported="true") that can be launched by other apps on the device.
• Sticky intent: A broadcast intent that remains in the system cache after it's sent, allowing any app to retrieve its contents.
• Signature permission: A permission whose protection level is set to signature, granted only to apps signed with the same developer key.
• onNewIntent: An activity lifecycle callback invoked when an activity is launched with FLAG_ACTIVITY_SINGLE_TOP and is already running at the top of the history stack.
• PendingIntent: A token granted to a foreign application (for example, system services) allowing it to execute a predefined Intent with the creator's permissions.
• Mutable PendingIntent: A PendingIntent whose underlying Intent parameters can be modified by the receiving application.
• ContentProvider: A component that encapsulates data and provides it to other applications via standard query/insert interfaces.
• IntentSanitizer: A utility class in AndroidX Core used to build a safe, sanitized copy of an incoming Intent by filtering out unauthorized components, actions, or extras.
• Intent redirection (forwarding): A vulnerability where an application receives an intent from an untrusted source and uses it to launch a private, non-exported component.

Prerequisites

• The agent MUST be able to describe the function and security implications of onCreate, onNewIntent, and the singleTop launch mode.
• The agent MUST be able to declare <activity>, <service>, <receiver>, and <provider> tags in AndroidManifest.xml and define their android:exported and android:permission attributes.
• The agent MUST be able to implement signature verification checks using PackageManager.

Limitations

• This skill focuses on local inter-component and inter-app communication security on the Android platform.
• This skill doesn't cover network security, web integration, or host-to-server security.

Setup and dependencies

• Android SDK: Minimum API Level 23 (Android 6.0) is required for standard hardware-backed keystore operations and component validation.
• AndroidX Core Library: androidx.core:core:1.9.0 or higher is mandatory to leverage IntentSanitizer.
• Standard API access: Standard Android PackageManager APIs are required for runtime component verification.

---

Intent security logic and decisions

1. Intent routing comparison

Evaluate the security features of different intent delivery methods:

Intent Delivery Method	Scope	Recommended Use Case
Explicit Intent (Internal)	App Private	Launching internal activities/services
Implicit Intent	System Wide	Launching system camera, dialer, or sharing
Local Broadcasts (LocalBroadcastManager) (DEPRECATED)	App Private	Internal asynchronous event routing. Deprecated: Use in-app observers like Kotlin Flows/SharedFlow, LiveData, or reactive patterns instead.
System Broadcasts	System Wide	Receiving system events (NFC, Bluetooth)

2. PendingIntent mutability flag options

Evaluate the security implications of PendingIntent mutability flags:

Flag Name	Mutability	Recommended Use Case
PendingIntent.FLAG_IMMUTABLE	Immutable	Default for almost all PendingIntents, such as alarms and notifications
PendingIntent.FLAG_MUTABLE	Mutable	Inline notifications replies, slice actions (requires explicit target intent)

3. Intent handling and redirection logic

IF (the component receives a nested Intent as an extra) { IF (AndroidX Core 1.9.0+ and higher is available) { MUST construct an IntentSanitizer to explicitly allowlist components, actions, data, and extras. MUST call sanitizeByThrowing() or sanitizeByFiltering() before launching. } ELSE { MUST verify that the nested Intent's target package matches the current application package. MUST verify that the target component of the nested Intent is publicly exported. } NEVER launch the nested Intent directly without validation. } ELSE IF (the component handles broadcasts) { MUST rely on the system's Protected Broadcast mechanism for system events (which guarantees the sender is the system framework). MUST protect custom receivers with signature-level permissions or use RECEIVER_NOT_EXPORTED for dynamic receivers to restrict the sender. }

4. PendingIntent security logic

IF (a PendingIntent is created for delivery to another application) { MUST use PendingIntent.FLAG_IMMUTABLE by default. IF (the PendingIntent must be mutable) { MUST set the explicit target component or package name on the base Intent. NEVER create an implicit, mutable PendingIntent. } }

5. ContentProvider security logic

IF (the ContentProvider is only for internal app use) { MUST set android:exported="false". } ELSE { MUST protect it with android:readPermission and android:writePermission. MUST set android:grantUriPermissions="false" unless temporary URL access is strictly required. }

6. Service caller verification logic

IF (an exported service communicates with trusted sister/partner apps) { MUST retrieve the calling UID using Binder.getCallingUid() and resolve it to package names using PackageManager.getPackagesForUid(). MUST verify that the calling package signature fingerprint matches your trusted certificate hash. }

---

Code and configuration patterns

1. Safe intent redirection (manual verification)

Validate the target of a nested intent before launching it when modern sanitization libraries are unavailable.

• Expected Inputs:
  • An incoming Intent containing a nested Intent extra named EXTRA_NESTED_INTENT.
• Expected Outputs:
  • Launches the target component if safe; throws SecurityException if validation fails.

fun safeIntentRedirectionManual() {
    val nestedIntent = IntentCompat.getParcelableExtra(intent, "EXTRA_NESTED_INTENT", Intent::class.java)
    if (nestedIntent != null) {
        // 1. Check for URI permission grants to prevent URI permission bypass
        val hasUriPermissionGrants = (
            nestedIntent.flags and (
                Intent.FLAG_GRANT_READ_URI_PERMISSION or
                    Intent.FLAG_GRANT_WRITE_URI_PERMISSION or
                    Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION or
                    Intent.FLAG_GRANT_PREFIX_URI_PERMISSION
                )
            ) != 0
        if (hasUriPermissionGrants) {
            throw SecurityException("Nested intent contains forbidden URI permission grant flags!")
        }

        val pm = packageManager
        val target = nestedIntent.resolveActivity(pm)
        if (target != null) {
            // 2. Verify target is within the same package
            if (target.packageName != packageName) {
                throw SecurityException("Cross-app intent redirection is forbidden!")
            }
            try {
                // 3. Verify target activity is exported
                val info = pm.getActivityInfo(target, 0)
                if (!info.exported) {
                    throw SecurityException("Target activity is private: ${target.className}")
                }
                // 4. Explicitly set the component to prevent intent interception
                nestedIntent.component = target
                // Safe to launch
                startActivity(nestedIntent)
            } catch (e: PackageManager.NameNotFoundException) {
                Log.e("Security", "Failed to resolve target activity", e)
            }
        }
    }
}

2. Safe intent redirection using IntentSanitizer

Filter or reject dynamic intents using AndroidX IntentSanitizer (AndroidX Core 1.9.0+).

• Expected Inputs:
  • An untrusted incoming Intent.
• Expected Outputs:
  • Intent: A sanitized copy containing only allowlisted components, categories, and actions. Throws SecurityException on violations if using sanitizeByThrowing().

fun safeIntentRedirectionSanitizer() {
    val untrustedIntent = IntentCompat.getParcelableExtra(intent, "EXTRA_NESTED_INTENT", Intent::class.java)
    if (untrustedIntent != null) {
        // Define the strict boundaries for allowed redirection target
        val sanitizer = IntentSanitizer.Builder()
            .allowComponent(ComponentName("com.example.app", "com.example.app.SafeTargetActivity")) // Explicitly allowed target
            .allowAction(Intent.ACTION_VIEW) // Explicitly allowed actions
            .allowDataWithAuthority("com.example.app.provider") // Allowed URI authority
            .allowType("text/plain") // Allowed mime type
            .allowExtra("user_display_name", String::class.java) // Safe type-enforced extras
            // Note: URI permission flags are NOT allowed, so the sanitizer will automatically strip or throw on them
            .build()

        try {
            // Option A: Throws SecurityException if the intent violates policies
            val safeIntent = sanitizer.sanitizeByThrowing(untrustedIntent)
            startActivity(safeIntent)
        } catch (e: SecurityException) {
            Log.e("SECURITY_ALERT", "Attempted launch of non-allowlisted intent blocked", e)
        }

        // Option B: Silently filter and launch only the authorized parts (no exception thrown)
        // val filteredIntent = sanitizer.sanitizeByFiltering(untrustedIntent)
        // startActivity(filteredIntent)
    }
}

3. Custom signature permission protection

Declare a custom signature-level permission in the manifest to secure family app communication.

• Expected Inputs: Manifest configuration.
• Expected Outputs: An activity that can only be launched by apps signed with the same developer certificate.

<permission
    android:name="com.example.snippets.permission.INTERNAL_COMMUNICATION"
    android:protectionLevel="signature" />

<activity
    android:name=".intents.InternalSharingActivity"
    android:exported="true"
    android:permission="com.example.snippets.permission.INTERNAL_COMMUNICATION">
    <intent-filter>
        <action android:name="com.example.snippets.ACTION_SHARE" />
        <category android:name="android.intent.category.DEFAULT" />
    </intent-filter>
</activity>

4. Safe onNewIntent lifecycle verification (warm boot protection)

Ensure that activities reusing dynamic intents (for example, in background launch paths) apply the same strict security filters inside onNewIntent.

• Expected Inputs:
  • newIntent (Intent): The newly delivered intent.
• Expected Outputs:
  • Executes processing logic only if the new intent passes security validation.

override fun onNewIntent(newIntent: Intent) {
    super.onNewIntent(newIntent)

    // Set the intent to ensure intent returns the new one
    intent = newIntent

    // Validate the intent payload
    if (validateIntent(newIntent)) {
        processIntentPayload(newIntent)
    } else {
        Log.w("SECURITY_ALERT", "Received invalid or insecure intent during warm boot")
    }
}

private fun validateIntent(intent: Intent): Boolean {
    return intent.hasExtra("VALID_PAYLOAD_MARKER")
}

5. Secure PendingIntent creation

Enforce immutability unless mutability is explicitly required.

• Expected Inputs (Immutable): An intent target.
• Expected Outputs (Immutable): A PendingIntent that cannot be altered by the receiver.
• Expected Inputs (Mutable): An intent with an explicit component set.
• Expected Outputs (Mutable): A mutable PendingIntent locked to a specific receiver component to prevent hijacking.

fun createPendingIntents(context: Context) {
    // 1. Secure Immutable PendingIntent (Default)
    val intent = Intent(context, TargetActivity::class.java)
    val pendingIntent = PendingIntent.getActivity(
        context,
        0,
        intent,
        PendingIntent.FLAG_IMMUTABLE or PendingIntent.FLAG_UPDATE_CURRENT
    )

    // 2. Secure Mutable PendingIntent (e.g., Notification Direct Reply)
    val mutableIntent = Intent().apply {
        // MUST set explicit target component to prevent redirection hijacking
        component = ComponentName(context, ReplyReceiver::class.java)
    }
    val mutablePendingIntent = PendingIntent.getBroadcast(
        context,
        0,
        mutableIntent,
        PendingIntent.FLAG_MUTABLE or PendingIntent.FLAG_UPDATE_CURRENT
    )
}

6. Secure ContentProvider configuration and queries

Expose a ContentProvider securely and parameterize queries to prevent SQL injection.

• Expected Inputs:
  • uri (Uri): The query URI.
  • projection (String[]): Columns to retrieve.
  • selection (String): Query criteria.
  • selectionArgs (String[]): Values mapping to selection placeholders (?).
• Expected Outputs:
  • Cursor: Filtered query results, strictly bound to projection maps.

<provider
    android:name=".intents.SecureDataProvider"
    android:authorities="com.example.snippets.provider"
    android:exported="true"
    android:readPermission="com.example.snippets.permission.READ_DATA"
    android:writePermission="com.example.snippets.permission.WRITE_DATA"
    android:grantUriPermissions="false" />

override fun query(
    uri: Uri,
    projection: Array<String>?,
    selection: String?,
    selectionArgs: Array<String>?,
    sortOrder: String?
): Cursor? {
    val queryBuilder = SQLiteQueryBuilder()
    queryBuilder.tables = tableName
    // Strict projection map to prevent querying unauthorized columns
    queryBuilder.projectionMap = mapOf(
        "_id" to "_id",
        "display_name" to "display_name"
    )
    // Enable strict validation (always available since minSdk is 36)
    queryBuilder.setStrict(true)
    queryBuilder.setStrictColumns(true)
    queryBuilder.setStrictGrammar(true)

    // MUST parameterize selection criteria; NEVER append selection strings directly
    val db = dbHelper.readableDatabase
    return queryBuilder.query(db, projection, selection, selectionArgs, null, null, sortOrder)
}

7. Service caller signature verification

Verify the calling application's signature before binding to a service.

• Expected Inputs:
  • intent (Intent): The binding request intent.
• Expected Outputs:
  • IBinder: Local binder instance if caller signature matches trusted partner; throws SecurityException otherwise.

class SecureBoundService : Service() {
    companion object {
        // Expected SHA-256 hash of the trusted app's signing certificate (Base64 encoded)
        private const val TRUSTED_PARTNER_SHA256 = "A1B2C3D4E5F6G7H8I9J0K1L2M3N4O5P6Q7R8S9T0U1V="
    }

    override fun onBind(intent: Intent): IBinder {
        // Return the binder. Do NOT perform signature verification in onBind() because
        // the binder connection is cached by Android, which can bypass checks on subsequent binds.
        return LocalBinder()
    }

    private fun enforceTrustedCaller() {
        val callingUid = Binder.getCallingUid()
        // Allow calls from the same application
        if (callingUid == Process.myUid()) {
            return
        }
        val pm = packageManager
        val packages = pm.getPackagesForUid(callingUid)

        if (packages.isNullOrEmpty() || !verifySignature(pm, packages[0])) {
            throw SecurityException("Access Denied: Caller signature is untrusted.")
        }
    }

    private fun verifySignature(pm: PackageManager, packageName: String): Boolean {
        try {
            val trustedSha256Raw = Base64.decode(TRUSTED_PARTNER_SHA256, Base64.DEFAULT)
            // API 28+ handles rotated certificates and avoids manual hashing.
            // Since minSdk is 36, this is always available.
            return pm.hasSigningCertificate(packageName, trustedSha256Raw, PackageManager.CERT_INPUT_SHA256)
        } catch (e: Exception) {
            Log.e("SECURITY_ERROR", "Verification failed for package: $packageName", e)
        }
        return false
    }

    inner class LocalBinder : Binder() {
        fun doSecureWork() {
            // Verify caller identity on every transaction method call
            enforceTrustedCaller()
            // Safe to proceed with sensitive operations
        }
    }
}

---

Error handling

Handle component binding, database queries, and intent redirection failures securely to avoid exposing internal structures.

fun safeErrorHandling(callingPackage: String?) {
    try {
        val payload = intent.getStringExtra("DATA_EXTRA") ?: throw IllegalArgumentException("Payload parameter missing.")
        // Create a specific target intent using the validated payload
        val targetIntent = Intent(this, TargetActivity::class.java).apply {
            putExtra("SECURE_PAYLOAD", payload)
        }
        startActivity(targetIntent)
    } catch (e: SecurityException) {
        // MUST log security violations for audit, but NEVER expose exception details to the user.
        Log.e("SECURITY_ERROR", "Unauthorized component transition blocked. Calling Package: ${callingPackage ?: "Unknown"}", e)
        // MUST provide generic user feedback.
        showFeedbackToUser("Process request failed: Access Denied.")
    } catch (e: IllegalArgumentException) {
        Log.w("INTEGRITY_WARNING", "Missing intent parameter", e)
    }
}

// Secure handling of ContentProvider queries on the client side:
try {
    val cursor = contentResolver.query(providerUri, projection, selection, selectionArgs, null)
} catch (e: SQLiteException) {
    Log.e("PROVIDER_ERROR", "ContentProvider database query failed", e)
    // Secure handling: prevent raw query syntax details from leaking to UI
}

---

Reporting guidelines

When this skill is executed to apply security hardening updates to a codebase, the agent MUST generate a structured "Best Practices and Security Alignment Update" report for the developer. The report must be written to the session artifact folder (or printed in the final response) and include:

1. Security alignment area: The category of improvement applied (for example, Safe Intent Redirection, Secure PendingIntent Configuration, ContentProvider Data Guarding).
2. Impact and priority: The potential safety risk addressed by the update (for example, Component Hijacking Prevention, Private Data Isolation).
3. Scope of changes: A list of all modified classes, XML files, and dependencies.
4. Implementation summary: Concrete details of the solution (for example, "Updated nested intent parsing to use the IntentSanitizer API with a strict component allowlist").
5. Code diff: Standard unified diffs showing the exact modifications.

Best practices and security alignment update template

Use the following markdown template when reporting changes to developers:

### Best practices and security alignment update: [Security Alignment Area]

*   **Improvement Description:** [Brief description of the hardening update and why it's recommended]
*   **Priority Level:** [High / Medium / Low]
*   **Alignment Action:** [Summary of updates, for example, converted to FLAG_IMMUTABLE]

#### Files modified
*   `[Relative path to File 1]`
*   `[Relative path to File 2]`

#### Implementation diff
```diff
// Insert Unified Diff here

Testing and verification

1. [Step 1 to verify the component behaves correctly, for example, run component unit test]
2. [Step 2 to verify regression safety] ```

---

Antipatterns

• NEVER launch a nested Intent received from an untrusted source without verifying its target package and exported status.
• NEVER use sticky broadcasts (sendStickyBroadcast).
• NEVER assume an exported component is safe because it runs in a background thread or performs internal checks.
• NEVER expose sensitive functionalities (like SSO authentication or payment processors) to components without signature-level permission restrictions.
• NEVER process incoming intents in onNewIntent without applying the same security controls as onCreate.
• NEVER create a mutable PendingIntent without setting an explicit target component in the base Intent.
• NEVER use dynamic string concatenation to construct selection blocks inside a ContentProvider query.
• NEVER use Binder.getCallingUid inside a BroadcastReceiver.onReceive to identify the sender of a broadcast, as it returns the receiver's own UID, not the sender's.

Best Practices

• MUST explicitly set android:exported="false" for all components that don't need external communication.
• MUST protect all exported components with custom permissions utilizing android:protectionLevel="signature" when communicating between family apps.
• MUST validate all incoming intent extras and handle missing parameters gracefully to prevent crashes.
• MUST rely on the system's Protected Broadcast mechanism for system events (for example, boot completed, package changes), as the system prevents untrusted apps from spoofing these actions.
• MUST protect custom broadcasts with signature-level permissions or use RECEIVER_NOT_EXPORTED for dynamic receivers to restrict the sender identity.
• MUST call setIntent(newIntent) inside onNewIntent() before processing payloads to keep active references updated.
• MUST use PendingIntent.FLAG_IMMUTABLE by default when constructing PendingIntent instances.
• MUST protect exported ContentProviders with readPermission and writePermission.
• MUST enforce parameterized selection structures in ContentProvider query/update methods.
• MUST verify the package signature fingerprint of binding applications at runtime inside exported services.
• MUST use androidx.core.content.IntentSanitizer to sanitize incoming dynamic intents before redirection, if AndroidX Core 1.9.0+ is imported in the project.