diff --git a/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/metamask/transport/MetamaskResponder.kt b/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/metamask/transport/MetamaskResponder.kt
index 709292ae..b966985d 100644
--- a/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/metamask/transport/MetamaskResponder.kt
+++ b/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/metamask/transport/MetamaskResponder.kt
@@ -4,8 +4,12 @@ import android.util.Log
 import io.novafoundation.nova.common.utils.LOG_TAG
 import io.novafoundation.nova.feature_dapp_impl.web3.webview.WebViewHolder
 import io.novafoundation.nova.runtime.multiNetwork.chain.model.ChainId
+import org.json.JSONObject
 
-sealed class MetamaskError(val errorCode: Int, message: String) : Throwable(message) {
+/**
+ * [publicMessage] is sent to the dApp page as is, so it must never carry internal error details.
+ */
+sealed class MetamaskError(val errorCode: Int, val publicMessage: String) : Throwable(publicMessage) {
 
     class Rejected : MetamaskError(4001, "Action rejected")
 
@@ -33,7 +37,8 @@ class MetamaskResponder(private val webViewHolder: WebViewHolder) {
     }
 
     fun respondError(messageId: String, error: MetamaskError) {
-        val js = "window.ethereum.sendRpcError($messageId, ${error.errorCode}, \"${error.message}\")"
+        val message = JSONObject.quote(error.publicMessage)
+        val js = "window.ethereum.sendRpcError($messageId, ${error.errorCode}, $message)"
 
         evaluateJs(js)
     }
diff --git a/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/polkadotJs/PolkadotJsResponder.kt b/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/polkadotJs/PolkadotJsResponder.kt
index 38ed5396..b9226b66 100644
--- a/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/polkadotJs/PolkadotJsResponder.kt
+++ b/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/polkadotJs/PolkadotJsResponder.kt
@@ -3,7 +3,9 @@ package io.novafoundation.nova.feature_dapp_impl.web3.polkadotJs
 import android.util.Log
 import io.novafoundation.nova.common.utils.LOG_TAG
 import io.novafoundation.nova.feature_dapp_impl.web3.Web3Responder
+import io.novafoundation.nova.feature_dapp_impl.web3.states.Web3StateMachineHost
 import io.novafoundation.nova.feature_dapp_impl.web3.webview.WebViewHolder
+import org.json.JSONObject
 
 class PolkadotJsResponder(
     private val webViewHolder: WebViewHolder
@@ -35,5 +37,20 @@ class PolkadotJsResponder(
 
     private fun successSubscription(id: String, result: String) = "window.walletExtension.onAppSubscription(\"$id\", $result)"
 
-    private fun failure(id: String, error: Throwable) = "window.walletExtension.onAppResponse(\"$id\", null, new Error(\"${error.message.orEmpty()}\"))"
+    private fun failure(id: String, error: Throwable): String {
+        val message = JSONObject.quote(publicErrorMessage(error))
+
+        return "window.walletExtension.onAppResponse(\"$id\", null, new Error($message))"
+    }
+
+    /**
+     * The page is untrusted, so it only ever receives a fixed message per known rejection reason,
+     * never the text of an arbitrary internal exception.
+     */
+    private fun publicErrorMessage(error: Throwable): String = when (error) {
+        Web3StateMachineHost.NotAuthorizedException -> "Rejected by user"
+        Web3StateMachineHost.SigningFailedException -> "Signing failed"
+        Web3StateMachineHost.PhishingDetectedException -> "Phishing detected!"
+        else -> "Request failed"
+    }
 }
diff --git a/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/polkadotJs/states/PhishingDetectedPolkadotJsState.kt b/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/polkadotJs/states/PhishingDetectedPolkadotJsState.kt
index bd5bcaed..a81c37aa 100644
--- a/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/polkadotJs/states/PhishingDetectedPolkadotJsState.kt
+++ b/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/polkadotJs/states/PhishingDetectedPolkadotJsState.kt
@@ -2,10 +2,11 @@ package io.novafoundation.nova.feature_dapp_impl.web3.polkadotJs.states
 
 import io.novafoundation.nova.feature_dapp_impl.web3.polkadotJs.PolkadotJsTransportRequest
 import io.novafoundation.nova.feature_dapp_impl.web3.states.PhishingDetectedState
+import io.novafoundation.nova.feature_dapp_impl.web3.states.Web3StateMachineHost
 
 class PhishingDetectedPolkadotJsState : PhishingDetectedState<PolkadotJsTransportRequest<*>, PolkadotJsState>(), PolkadotJsState {
 
     override fun rejectError(): Throwable {
-        return IllegalAccessException("Phishing detected!")
+        return Web3StateMachineHost.PhishingDetectedException
     }
 }
diff --git a/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/states/Web3ExtensionStateMachine.kt b/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/states/Web3ExtensionStateMachine.kt
index bd68f700..05b054cb 100644
--- a/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/states/Web3ExtensionStateMachine.kt
+++ b/feature-dapp-impl/src/main/java/io/novafoundation/nova/feature_dapp_impl/web3/states/Web3ExtensionStateMachine.kt
@@ -42,6 +42,7 @@ interface Web3StateMachineHost {
 
     object NotAuthorizedException : Exception("Rejected by user")
     object SigningFailedException : Exception("Signing failed")
+    object PhishingDetectedException : Exception("Phishing detected!")
 
     val selectedAccount: Flow<MetaAccount>
     val currentPageAnalyzed: Flow<BrowserPageAnalyzed>