[PM-27752] Add certificate signature verification to AuthenticatorBridge (#6126)

Co-authored-by: Claude <noreply@anthropic.com>

authenticatorbridge/CHANGELOG.md

@@ -7,6 +7,13 @@ v1.1.0 (pending)
 
 ### Bug Fixes
 
+v1.0.2
+--------
+
+### Bug Fixes
+
+- Added cryptographic certificate signature verification to prevent malicious applications from spoofing Password Manager package names and intercepting TOTP secrets (VULN-314).
+
 v1.0.1
 --------
 

authenticatorbridge/build.gradle.kts

@@ -1,7 +1,7 @@
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 
 // For more info on versioning, see the README.
-val version = "1.0.1"
+val version = "1.0.2"
 
 plugins {
     alias(libs.plugins.android.library)
@@ -66,6 +66,7 @@ dependencies {
     implementation(libs.androidx.lifecycle.process)
     implementation(libs.kotlinx.serialization)
     implementation(libs.kotlinx.coroutines.core)
+    implementation(libs.timber)
 
     // Test environment dependencies:
     testImplementation(platform(libs.junit.bom))

authenticatorbridge/src/debug/res/values/strings.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string-array name="known_bitwarden_certs">
+        <!-- This is the SHA-256 digest for Debug signing key of the Bitwarden App debug
+        variant: -->
+        <item>0418ff9b3a883040ee3e1931093a7edca19b2f87f455388f28906bf262e32de7</item>
+    </string-array>
+</resources>

authenticatorbridge/src/main/kotlin/com/bitwarden/authenticatorbridge/factory/AuthenticatorBridgeFactory.kt

@@ -5,6 +5,7 @@ import com.bitwarden.authenticatorbridge.manager.AuthenticatorBridgeManager
 import com.bitwarden.authenticatorbridge.manager.AuthenticatorBridgeManagerImpl
 import com.bitwarden.authenticatorbridge.manager.model.AuthenticatorBridgeConnectionType
 import com.bitwarden.authenticatorbridge.provider.SymmetricKeyStorageProvider
+import com.bitwarden.authenticatorbridge.util.PasswordManagerSignatureVerifierImpl
 
 /**
  * Factory for supplying implementation instances of Authenticator Bridge SDK interfaces.
@@ -29,5 +30,6 @@ class AuthenticatorBridgeFactory(
         context = applicationContext,
         connectionType = connectionType,
         symmetricKeyStorageProvider = symmetricKeyStorageProvider,
+        passwordManagerSignatureVerifier = PasswordManagerSignatureVerifierImpl(applicationContext),
     )
 }

authenticatorbridge/src/main/kotlin/com/bitwarden/authenticatorbridge/manager/AuthenticatorBridgeManagerImpl.kt

@@ -4,7 +4,6 @@ import android.content.ComponentName
 import android.content.Context
 import android.content.Intent
 import android.content.ServiceConnection
-import android.content.pm.PackageManager.NameNotFoundException
 import android.os.Build
 import android.os.IBinder
 import androidx.lifecycle.DefaultLifecycleObserver
@@ -19,6 +18,7 @@ import com.bitwarden.authenticatorbridge.model.EncryptedSharedAccountData
 import com.bitwarden.authenticatorbridge.provider.AuthenticatorBridgeCallbackProvider
 import com.bitwarden.authenticatorbridge.provider.StubAuthenticatorBridgeCallbackProvider
 import com.bitwarden.authenticatorbridge.provider.SymmetricKeyStorageProvider
+import com.bitwarden.authenticatorbridge.util.PasswordManagerSignatureVerifier
 import com.bitwarden.authenticatorbridge.util.decrypt
 import com.bitwarden.authenticatorbridge.util.encrypt
 import com.bitwarden.authenticatorbridge.util.toFingerprint
@@ -37,6 +37,7 @@ private const val AUTHENTICATOR_BRIDGE_SERVICE_CLASS =
  * @param connectionType Specifies which build variant to connect to.
  * @param symmetricKeyStorageProvider Provides access to local storage of the symmetric encryption
  * key.
+ * @param passwordManagerSignatureVerifier Verifies the authenticity of the Password Manager app.
  * @param callbackProvider Provides a way to construct a service callback that can be mocked in
  * tests.
  * @param processLifecycleOwner Lifecycle owner that is used to listen for start/stop
@@ -45,6 +46,7 @@ private const val AUTHENTICATOR_BRIDGE_SERVICE_CLASS =
 internal class AuthenticatorBridgeManagerImpl(
     private val connectionType: AuthenticatorBridgeConnectionType,
     private val symmetricKeyStorageProvider: SymmetricKeyStorageProvider,
+    private val passwordManagerSignatureVerifier: PasswordManagerSignatureVerifier,
     callbackProvider: AuthenticatorBridgeCallbackProvider =
         StubAuthenticatorBridgeCallbackProvider(),
     context: Context,
@@ -67,6 +69,7 @@ internal class AuthenticatorBridgeManagerImpl(
                 !isBuildVersionAtLeast(Build.VERSION_CODES.S) -> {
                     AccountSyncState.OsVersionNotSupported
                 }
+
                 !isBitwardenAppInstalled() -> AccountSyncState.AppNotInstalled
                 else -> AccountSyncState.Loading
             },
@@ -243,13 +246,11 @@ internal class AuthenticatorBridgeManagerImpl(
         }
     }
 
-    private fun isBitwardenAppInstalled(): Boolean =
-        // Check to see if correct Bitwarden app is installed:
-        try {
-            applicationContext.packageManager.getPackageInfo(connectionType.toPackageName(), 0)
-            true
-        } catch (e: NameNotFoundException) {
-            false
+    private fun isBitwardenAppInstalled(): Boolean {
+        // Verify the Password Manager app is installed and has a valid signature
+        return passwordManagerSignatureVerifier.isValidPasswordManagerApp(
+            packageName = connectionType.toPackageName(),
+        )
     }
 }
 

authenticatorbridge/src/main/kotlin/com/bitwarden/authenticatorbridge/util/PasswordManagerSignatureVerifier.kt

@@ -0,0 +1,14 @@
+package com.bitwarden.authenticatorbridge.util
+
+/**
+ * Verifies that a Password Manager application is authentic by validating its signing certificate.
+ */
+internal interface PasswordManagerSignatureVerifier {
+    /**
+     * Validates the signature of the specified Password Manager package.
+     *
+     * @param packageName The package name to verify
+     * @return true if the package has a valid signature, false otherwise
+     */
+    fun isValidPasswordManagerApp(packageName: String): Boolean
+}

authenticatorbridge/src/main/kotlin/com/bitwarden/authenticatorbridge/util/PasswordManagerSignatureVerifierImpl.kt

@@ -0,0 +1,128 @@
+package com.bitwarden.authenticatorbridge.util
+
+import android.content.Context
+import android.content.pm.PackageManager
+import com.bitwarden.annotation.OmitFromCoverage
+import com.bitwarden.authenticatorbridge.R
+import timber.log.Timber
+import java.security.MessageDigest
+import java.security.NoSuchAlgorithmException
+
+/**
+ * Default implementation of [PasswordManagerSignatureVerifier].
+ *
+ * Validates Password Manager applications by verifying their cryptographic signing certificate
+ * against a whitelist of known-good certificate hashes.
+ *
+ * This addresses VULN-314: Insufficient package name validation allows TOTP secret harvesting
+ * when malicious applications spoof legitimate package names without proper cryptographic
+ * identity verification.
+ *
+ * Security Considerations:
+ * - Rejects apps with multiple signers to prevent signature rotation attacks
+ * - Uses GET_SIGNING_CERTIFICATES (API 28+) for secure certificate retrieval
+ * - Validates SHA-256 certificate fingerprint against hardcoded whitelist
+ * - Fails closed on any validation error or exception
+ *
+ * References:
+ * [1] Android AOSP. "APK Signature Scheme v3."
+ *     https://source.android.com/docs/security/features/apksigning/v3
+ *     "Multiple signers are not supported and Google Play does not publish apps signed
+ *     with multiple certificates"
+ *
+ * [2] Android Developers. "SigningInfo API Reference."
+ *     https://developer.android.com/reference/android/content/pm/SigningInfo
+ *     Deprecation of GET_SIGNATURES in favor of GET_SIGNING_CERTIFICATES for improved security.
+ *
+ * [3] OWASP MASTG. "MASTG-TEST-0038: Making Sure that the App is Properly Signed."
+ *     https://mas.owasp.org/MASTG/tests/android/MASVS-RESILIENCE/MASTG-TEST-0038/
+ *     Best practices for signature validation and integrity verification.
+ *
+ * [4] GuardSquare. "Janus Vulnerability (CVE-2017-13156)."
+ *     https://www.guardsquare.com/blog/janus-vulnerability
+ *     Historical context: signature bypass attacks mitigated by v2/v3 schemes.
+ *
+ * @param context Android context for accessing PackageManager and resources
+ */
+@OmitFromCoverage
+internal class PasswordManagerSignatureVerifierImpl(
+    private val context: Context,
+) : PasswordManagerSignatureVerifier {
+
+    private val knownPasswordManagerCertificates: List<String> by lazy {
+        context.resources
+            .getStringArray(R.array.known_bitwarden_certs)
+            .toList()
+    }
+
+    override fun isValidPasswordManagerApp(packageName: String): Boolean {
+        return try {
+            val packageManager = context.packageManager
+            val packageInfo = packageManager.getPackageInfo(
+                packageName,
+                PackageManager.GET_SIGNING_CERTIFICATES,
+            )
+
+            val signingInfo = packageInfo.signingInfo ?: run {
+                Timber.w(
+                    "Signature verification failed: signingInfo is null for package $packageName",
+                )
+                return false
+            }
+
+            // Reject multiple signers to prevent signature rotation attacks.
+            // Bitwarden uses stable, long-lived signing certificates and never performs rotation.
+            // Any multi-signer scenario indicates:
+            // - Malicious rotation attempt
+            // - Compromised/tampered APK
+            // - Non-genuine Bitwarden application
+            // See: https://source.android.com/docs/security/features/apksigning/v3
+            if (signingInfo.hasMultipleSigners()) {
+                Timber.w(
+                    "Signature verification failed: multiple signers detected for $packageName",
+                )
+                return false
+            }
+
+            val signature = signingInfo.apkContentsSigners.first()
+            val sha256 = MessageDigest.getInstance("SHA-256")
+            val certHash = sha256.digest(signature.toByteArray())
+            val certHashHex = certHash.joinToString("") { "%02x".format(it) }
+
+            // Use constant-time comparison to prevent timing attacks
+            val isValid = knownPasswordManagerCertificates.any { knownCert ->
+                MessageDigest.isEqual(
+                    knownCert.toByteArray(),
+                    certHashHex.toByteArray(),
+                )
+            }
+            if (!isValid) {
+                Timber.w(
+                    "Signature verification failed for $packageName: unknown certificate hash",
+                )
+            }
+            isValid
+        } catch (e: PackageManager.NameNotFoundException) {
+            Timber.w(e, "Signature verification failed for $packageName: package not found")
+            false
+        } catch (e: SecurityException) {
+            Timber.e(
+                e,
+                "Signature verification failed for $packageName: security exception",
+            )
+            false
+        } catch (e: NoSuchAlgorithmException) {
+            Timber.e(
+                e,
+                "Signature verification failed for $packageName: SHA-256 unavailable",
+            )
+            false
+        } catch (e: NoSuchElementException) {
+            Timber.e(
+                e,
+                "Signature verification failed for $packageName: no signing certificates",
+            )
+            false
+        }
+    }
+}

authenticatorbridge/src/release/res/values/strings.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string-array name="known_bitwarden_certs">
+        <!-- This is the SHA-256 digest for Google Play signing key of the Bitwarden App release
+        variant: -->
+        <item>24e06c04c208048f19f1c993b4dda4430ea8b06db8375ea0e37b834696b9ac3a</item>
+
+        <!-- This is the SHA-256 digest for F-Droid App Distribution signing key of the
+         Bitwarden App release variant: -->
+        <item>de6ec91431557995297bf3e65bc80349bc603a04708160618c86bc9994171c90</item>
+    </string-array>
+</resources>

authenticatorbridge/src/test/kotlin/com/bitwarden/authenticatorbridge/manager/AuthenticatorBridgeManagerTest.kt

@@ -3,7 +3,6 @@ package com.bitwarden.authenticatorbridge.manager
 import android.content.Context
 import android.content.Intent
 import android.content.ServiceConnection
-import android.content.pm.PackageManager.NameNotFoundException
 import android.os.Build
 import com.bitwarden.authenticatorbridge.IAuthenticatorBridgeService
 import com.bitwarden.authenticatorbridge.IAuthenticatorBridgeServiceCallback
@@ -13,6 +12,7 @@ import com.bitwarden.authenticatorbridge.model.EncryptedSharedAccountData
 import com.bitwarden.authenticatorbridge.model.SharedAccountData
 import com.bitwarden.authenticatorbridge.util.FakeLifecycleOwner
 import com.bitwarden.authenticatorbridge.util.FakeSymmetricKeyStorageProvider
+import com.bitwarden.authenticatorbridge.util.PasswordManagerSignatureVerifier
 import com.bitwarden.authenticatorbridge.util.TestAuthenticatorBridgeCallbackProvider
 import com.bitwarden.authenticatorbridge.util.decrypt
 import com.bitwarden.authenticatorbridge.util.generateSecretKey
@@ -44,6 +44,9 @@ class AuthenticatorBridgeManagerTest {
         } returns mockk()
     }
     private val mockBridgeService: IAuthenticatorBridgeService = mockk()
+    private val mockPasswordManagerSignatureVerifier = mockk<PasswordManagerSignatureVerifier> {
+        every { isValidPasswordManagerApp(any()) } returns true
+    }
     private val fakeLifecycleOwner = FakeLifecycleOwner()
     private val fakeSymmetricKeyStorageProvider = FakeSymmetricKeyStorageProvider()
     private val testAuthenticatorBridgeCallbackProvider = TestAuthenticatorBridgeCallbackProvider()
@@ -65,6 +68,7 @@ class AuthenticatorBridgeManagerTest {
             context = context,
             connectionType = AuthenticatorBridgeConnectionType.DEV,
             symmetricKeyStorageProvider = fakeSymmetricKeyStorageProvider,
+            passwordManagerSignatureVerifier = mockPasswordManagerSignatureVerifier,
             callbackProvider = testAuthenticatorBridgeCallbackProvider,
             processLifecycleOwner = fakeLifecycleOwner,
         )
@@ -86,12 +90,13 @@ class AuthenticatorBridgeManagerTest {
     @Test
     fun `initial AccountSyncState should be AppNotInstalled when Bitwarden app is not present`() {
         every {
-            context.packageManager.getPackageInfo("com.x8bit.bitwarden.dev", 0)
-        } throws NameNotFoundException()
+            mockPasswordManagerSignatureVerifier.isValidPasswordManagerApp(any())
+        } returns false
         val manager = AuthenticatorBridgeManagerImpl(
             context = context,
             connectionType = AuthenticatorBridgeConnectionType.DEV,
             symmetricKeyStorageProvider = fakeSymmetricKeyStorageProvider,
+            passwordManagerSignatureVerifier = mockPasswordManagerSignatureVerifier,
             callbackProvider = testAuthenticatorBridgeCallbackProvider,
             processLifecycleOwner = fakeLifecycleOwner,
         )
@@ -127,10 +132,12 @@ class AuthenticatorBridgeManagerTest {
 
     @Test
     fun `onStart when Bitwarden app is not present should set state to AppNotInstalled`() {
-        val mockIntent: Intent = mockk()
+        // Mock verifier to return false (app not valid/installed)
         every {
-            context.packageManager.getPackageInfo("com.x8bit.bitwarden.dev", 0)
-        } throws NameNotFoundException()
+            mockPasswordManagerSignatureVerifier.isValidPasswordManagerApp(any())
+        } returns false
+
+        val mockIntent: Intent = mockk()
         every {
             anyConstructed<Intent>().setComponent(any())
         } returns mockIntent
@@ -578,6 +585,7 @@ class AuthenticatorBridgeManagerTest {
                 context = context,
                 connectionType = AuthenticatorBridgeConnectionType.DEV,
                 symmetricKeyStorageProvider = fakeSymmetricKeyStorageProvider,
+                passwordManagerSignatureVerifier = mockPasswordManagerSignatureVerifier,
                 callbackProvider = testAuthenticatorBridgeCallbackProvider,
                 processLifecycleOwner = fakeLifecycleOwner,
             )