diff --git a/tests/api/specs/hasura/app-verification.spec.ts b/tests/api/specs/hasura/app-verification.spec.ts
index 5ed5fb4ee..6b7616205 100644
--- a/tests/api/specs/hasura/app-verification.spec.ts
+++ b/tests/api/specs/hasura/app-verification.spec.ts
@@ -20,7 +20,8 @@ describe.skip("Hasura API - App Verification", () => {
 
     beforeAll(async () => {
       // Set required AWS environment variables for tests
-      process.env.ASSETS_S3_BUCKET_NAME = "world-id-assets-staging";
+      process.env.ASSETS_S3_BUCKET_NAME =
+        process.env.ASSETS_S3_BUCKET_NAME || "world-id-assets-staging";
       process.env.ASSETS_S3_REGION = "us-east-1";
 
       // Create test app and metadata
diff --git a/tests/api/specs/hasura/get-image.spec.ts b/tests/api/specs/hasura/get-image.spec.ts
index 4e2c9e2cf..39c933be7 100644
--- a/tests/api/specs/hasura/get-image.spec.ts
+++ b/tests/api/specs/hasura/get-image.spec.ts
@@ -36,7 +36,8 @@ describe("Hasura API - Get Image", () => {
 
     beforeAll(async () => {
       // Set required AWS environment variables for tests
-      process.env.ASSETS_S3_BUCKET_NAME = "world-id-assets-staging";
+      process.env.ASSETS_S3_BUCKET_NAME =
+        process.env.ASSETS_S3_BUCKET_NAME || "world-id-assets-staging";
       process.env.ASSETS_S3_REGION = "us-east-1";
 
       // Create test team and user
diff --git a/tests/api/specs/hasura/get-unverified-images.spec.ts b/tests/api/specs/hasura/get-unverified-images.spec.ts
index 0a33a3550..1d692141d 100644
--- a/tests/api/specs/hasura/get-unverified-images.spec.ts
+++ b/tests/api/specs/hasura/get-unverified-images.spec.ts
@@ -32,7 +32,8 @@ describe("Hasura API - Get Unverified Images", () => {
 
     beforeAll(async () => {
       // Set required AWS environment variables for tests
-      process.env.ASSETS_S3_BUCKET_NAME = "world-id-assets-staging";
+      process.env.ASSETS_S3_BUCKET_NAME =
+        process.env.ASSETS_S3_BUCKET_NAME || "world-id-assets-staging";
       process.env.ASSETS_S3_REGION = "us-east-1";
 
       // Create test team and user
diff --git a/web/api/helpers/kms-eth.ts b/web/api/helpers/kms-eth.ts
index 0644cf1ca..d4e09d4d2 100644
--- a/web/api/helpers/kms-eth.ts
+++ b/web/api/helpers/kms-eth.ts
@@ -22,7 +22,7 @@ import {
   toBeHex,
   zeroPadValue,
 } from "ethers";
-import { scheduleKeyDeletion } from "./kms";
+import { resolveKeyId, scheduleKeyDeletion } from "./kms";
 
 // secp256k1 curve order
 const SECP256K1_N = BigInt(
@@ -187,7 +187,7 @@ export async function getEthAddressFromKMS(
   keyId: string,
 ): Promise<string> {
   const { PublicKey } = await client.send(
-    new GetPublicKeyCommand({ KeyId: keyId }),
+    new GetPublicKeyCommand({ KeyId: resolveKeyId(keyId) }),
   );
 
   if (!PublicKey) {
@@ -214,7 +214,7 @@ async function signWithKms(
 ): Promise<EthSignature> {
   const { Signature: derSignature } = await client.send(
     new SignCommand({
-      KeyId: keyId,
+      KeyId: resolveKeyId(keyId),
       Message: digest,
       MessageType: "DIGEST",
       SigningAlgorithm: "ECDSA_SHA_256",
@@ -273,7 +273,7 @@ export async function createManagerKey(
       }),
     );
 
-    const keyId = KeyMetadata?.KeyId;
+    const keyId = KeyMetadata?.Arn ?? KeyMetadata?.KeyId;
     const createdAt = KeyMetadata?.CreationDate;
 
     if (!keyId || !createdAt) {
diff --git a/web/api/helpers/kms.ts b/web/api/helpers/kms.ts
index 75a1ee7c6..fbe26d8e2 100644
--- a/web/api/helpers/kms.ts
+++ b/web/api/helpers/kms.ts
@@ -31,6 +31,30 @@ export const getKMSClient = async (region?: string) => {
   });
 };
 
+/**
+ * Resolves a KMS key reference to a full ARN for cross-account access.
+ *
+ * - Full ARN (`arn:aws:kms:...`): returned as-is (new keys or already resolved)
+ * - Bare key ID (UUID): if `KMS_LEGACY_ACCOUNT_ID` is set, constructs a full
+ *   ARN pointing to the legacy account; otherwise returns as-is
+ *
+ * This enables a seamless migration period where the application runs in a new
+ * AWS account but still uses KMS keys that remain in the old account.
+ */
+export function resolveKeyId(keyId: string, region?: string): string {
+  if (keyId.startsWith("arn:")) {
+    return keyId;
+  }
+
+  const legacyAccountId = process.env.KMS_LEGACY_ACCOUNT_ID;
+  if (!legacyAccountId) {
+    return keyId;
+  }
+
+  const resolvedRegion = region ?? process.env.AWS_REGION_NAME ?? "eu-west-1";
+  return `arn:aws:kms:${resolvedRegion}:${legacyAccountId}:key/${keyId}`;
+}
+
 export const createKMSKey = async (
   client: KMSClient,
   alg: KeySpec,
@@ -45,7 +69,7 @@ export const createKMSKey = async (
       }),
     );
 
-    const keyId = KeyMetadata?.KeyId;
+    const keyId = KeyMetadata?.Arn ?? KeyMetadata?.KeyId;
     const createdAt = KeyMetadata?.CreationDate;
 
     if (keyId && createdAt) {
@@ -70,7 +94,7 @@ export const getKMSKeyStatus = async (client: KMSClient, keyId: string) => {
   try {
     const { KeyMetadata } = await client.send(
       new DescribeKeyCommand({
-        KeyId: keyId,
+        KeyId: resolveKeyId(keyId),
       }),
     );
     return KeyMetadata?.Enabled;
@@ -97,7 +121,7 @@ export const signJWTWithKMSKey = async (
 
     const response = await client.send(
       new SignCommand({
-        KeyId: kms_id,
+        KeyId: resolveKeyId(kms_id),
         Message: new Uint8Array(Buffer.from(encodedHeaderPayload)),
         MessageType: "RAW",
         SigningAlgorithm: "RSASSA_PKCS1_V1_5_SHA_256",
@@ -122,7 +146,7 @@ export const scheduleKeyDeletion = async (client: KMSClient, keyId: string) => {
   try {
     await client.send(
       new ScheduleKeyDeletionCommand({
-        KeyId: keyId,
+        KeyId: resolveKeyId(keyId),
         PendingWindowInDays: 7, // Note: 7 is the minimum allowed value
       }),
     );
diff --git a/web/lib/utils.ts b/web/lib/utils.ts
index 0914d62aa..a07b7682b 100644
--- a/web/lib/utils.ts
+++ b/web/lib/utils.ts
@@ -259,8 +259,12 @@ export const isValidHostName = (request: Request) => {
     return false;
   }
 
-  // Skip check for development
-  if (process.env.NODE_ENV === "development") {
+  // Skip check for development and staging (staging may not have custom domains)
+  // TODO(CORPLAT-689): Remove staging bypass after DNS cutover
+  if (
+    process.env.NODE_ENV === "development" ||
+    process.env.NEXT_PUBLIC_APP_ENV === "staging"
+  ) {
     return true;
   }
   const cdnHost = process.env.NEXT_PUBLIC_IMAGES_CDN_URL;