From ff64cf5063b610d4ea56392158ed00e29ef20fdf Mon Sep 17 00:00:00 2001
From: Andreas Coroiu <acoroiu@bitwarden.com>
Date: Thu, 28 Aug 2025 13:30:57 +0200
Subject: [PATCH] Fix a cache race condition in local backed session storage
 (#16177)

* fix: cache race condition

* fix: typo and order

* feat: tweak log message
---
 .../local-backed-session-storage.service.ts   | 25 +++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/apps/browser/src/platform/services/local-backed-session-storage.service.ts b/apps/browser/src/platform/services/local-backed-session-storage.service.ts
index 978b993fa4d..9e808de0fd0 100644
--- a/apps/browser/src/platform/services/local-backed-session-storage.service.ts
+++ b/apps/browser/src/platform/services/local-backed-session-storage.service.ts
@@ -73,8 +73,29 @@ export class LocalBackedSessionStorageService
 
     const value = await this.getLocalSessionValue(await this.sessionKey.get(), key);
 
-    this.cache[key] = value;
-    return value as T;
+    if (this.cache[key] === undefined && value !== undefined) {
+      // Cache is still empty and we just got a value from local/session storage, cache it.
+      this.cache[key] = value;
+      return value as T;
+    } else if (this.cache[key] === undefined && value === undefined) {
+      // Cache is still empty and we got nothing from local/session storage, no need to modify cache.
+      return value as T;
+    } else if (this.cache[key] !== undefined && value !== undefined) {
+      // Conflict, somebody wrote to the cache while we were reading from storage
+      // but we also got a value from storage. We assume the cache is more up to date
+      // and use that value.
+      this.logService.warning(
+        `Conflict while reading from local session storage, both cache and storage have values. Key: ${key}. Using cached value.`,
+      );
+      return this.cache[key] as T;
+    } else if (this.cache[key] !== undefined && value === undefined) {
+      // Cache was filled after the local/session storage read completed. We got null
+      // from the storage read, but we have a value from the cache, use that.
+      this.logService.warning(
+        `Conflict while reading from local session storage, cache has value but storage does not. Key: ${key}. Using cached value.`,
+      );
+      return this.cache[key] as T;
+    }
   }
 
   async has(key: string): Promise<boolean> {