From 49fb07c1bc0017b74d572e7f6ac919a0e560d695 Mon Sep 17 00:00:00 2001
From: Cayman <caymannava@gmail.com>
Date: Tue, 17 May 2022 10:11:33 -0500
Subject: [PATCH] Ensure light client update is in a single period

---
 packages/lodestar/src/chain/lightClient/index.ts | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/packages/lodestar/src/chain/lightClient/index.ts b/packages/lodestar/src/chain/lightClient/index.ts
index 1747671e9b83..353b7fc9b9ab 100644
--- a/packages/lodestar/src/chain/lightClient/index.ts
+++ b/packages/lodestar/src/chain/lightClient/index.ts
@@ -428,6 +428,8 @@ export class LightClientServer {
    * ```
    *
    * 3. On new blocks use `block.body.sync_aggregate`, `block.parent_root` and `block.slot - 1`
+   *
+   * @param syncPeriod The sync period of the sync aggregate and signed block root
    */
   private async onSyncAggregate(
     syncPeriod: SyncPeriod,
@@ -445,6 +447,11 @@ export class LightClientServer {
       }
     }
 
+    const attestedPeriod = computeSyncPeriodAtSlot(attestedData.attestedHeader.slot);
+    if (syncPeriod !== attestedPeriod) {
+      throw new Error("attested data period different than signature period");
+    }
+
     const headerUpdate: routes.lightclient.LightclientHeaderUpdate = {
       attestedHeader: attestedData.attestedHeader,
       syncAggregate,
@@ -506,7 +513,7 @@ export class LightClientServer {
       // Only checkpoint candidates are stored, and not all headers are guaranteed to be available
       const finalizedCheckpointRoot = attestedData.finalizedCheckpoint.root as Uint8Array;
       const finalizedHeader = await this.getFinalizedHeader(finalizedCheckpointRoot);
-      if (finalizedHeader) {
+      if (finalizedHeader && computeSyncPeriodAtSlot(finalizedHeader.slot) == syncPeriod) {
         // If finalizedHeader is available (should be most times) create a finalized update
         newPartialUpdate = {...attestedData, finalizedHeader, syncAggregate};
       } else {