diff --git a/packages/features/auth/__mocks__/getServerSession.mocks.ts b/packages/features/auth/__mocks__/getServerSession.mocks.ts
new file mode 100644
index 0000000000..754cbeb88f
--- /dev/null
+++ b/packages/features/auth/__mocks__/getServerSession.mocks.ts
@@ -0,0 +1,157 @@
+import type { Mock } from "vitest";
+import { vi } from "vitest";
+import { mockDeep, mockReset, type DeepMockProxy } from "vitest-mock-extended";
+
+import type { PrismaClient } from "@calcom/prisma";
+import type { User } from "@calcom/prisma/client";
+
+// Types
+type LoggerInstance = {
+  warn: Mock;
+  error: Mock;
+  debug: Mock;
+};
+
+type LoggerMock = {
+  default: {
+    getSubLogger: () => LoggerInstance;
+  };
+};
+
+// JWT token structure used by NextAuth
+interface MockToken {
+  sub: string;
+  email: string;
+  name: string;
+  exp: number;
+  belongsToActiveTeam: boolean;
+  org: null;
+  orgAwareUsername: string | null;
+  profileId: number | null;
+  upId: string;
+  impersonatedBy?: { id: number };
+}
+
+// Prisma mock instance
+const prismaMock: DeepMockProxy<PrismaClient> = mockDeep<PrismaClient>();
+
+function resetPrismaMock(): void {
+  mockReset(prismaMock);
+}
+
+function createLoggerMock(): LoggerMock {
+  const loggerInstance: LoggerInstance = {
+    warn: vi.fn(),
+    error: vi.fn(),
+    debug: vi.fn(),
+  };
+  return {
+    default: {
+      getSubLogger: (): LoggerInstance => loggerInstance,
+    },
+  };
+}
+
+function createPrismaMock(): { default: DeepMockProxy<PrismaClient> } {
+  return { default: prismaMock };
+}
+
+function createLicenseKeyMock(): {
+  LicenseKeySingleton: { getInstance: Mock };
+} {
+  return {
+    LicenseKeySingleton: {
+      getInstance: vi.fn().mockResolvedValue({
+        checkLicense: vi.fn().mockResolvedValue(false),
+      }),
+    },
+  };
+}
+
+function createDeploymentRepositoryMock(): {
+  DeploymentRepository: new (_prisma: PrismaClient) => object;
+} {
+  return {
+    DeploymentRepository: class MockDeploymentRepository {},
+  };
+}
+
+function createUserRepositoryMock(): {
+  UserRepository: new (_prisma: PrismaClient) => {
+    enrichUserWithTheProfile: (params: { user: User }) => Promise<User & { profile: null }>;
+  };
+} {
+  return {
+    UserRepository: class MockUserRepository {
+      enrichUserWithTheProfile({ user }: { user: User }): Promise<User & { profile: null }> {
+        return Promise.resolve({
+          ...user,
+          profile: null,
+        });
+      }
+    },
+  };
+}
+
+function createAvatarUrlMock(): { getUserAvatarUrl: Mock } {
+  return {
+    getUserAvatarUrl: vi.fn().mockReturnValue("https://example.com/avatar.png"),
+  };
+}
+
+function createSafeStringifyMock(): { safeStringify: Mock } {
+  return {
+    safeStringify: vi.fn().mockReturnValue("{}"),
+  };
+}
+
+function createGetTokenMock(): { getToken: Mock } {
+  return { getToken: vi.fn() };
+}
+
+// Creates a mock User with only the fields used by getServerSession
+function createMockUser(overrides: Partial<User> = {}): User {
+  return {
+    id: 5,
+    email: "user@example.com",
+    name: "Test User",
+    username: "testuser",
+    emailVerified: new Date(),
+    completedOnboarding: true,
+    role: "USER",
+    avatarUrl: null,
+    locale: "en",
+    ...overrides,
+  } as User;
+}
+
+function createMockToken(overrides: Partial<MockToken> = {}): MockToken {
+  return {
+    sub: "5",
+    email: "user@example.com",
+    name: "Test User",
+    exp: Math.floor(Date.now() / 1000) + 3600,
+    belongsToActiveTeam: false,
+    org: null,
+    orgAwareUsername: null,
+    profileId: null,
+    upId: "usr-5",
+    ...overrides,
+  };
+}
+
+export type { MockToken };
+export {
+  prismaMock,
+  resetPrismaMock,
+  createLoggerMock,
+  createPrismaMock,
+  createLicenseKeyMock,
+  createDeploymentRepositoryMock,
+  createUserRepositoryMock,
+  createAvatarUrlMock,
+  createSafeStringifyMock,
+  createGetTokenMock,
+  createMockUser,
+  createMockToken,
+};
diff --git a/packages/features/auth/lib/getServerSession.test.ts b/packages/features/auth/lib/getServerSession.test.ts
new file mode 100644
index 0000000000..8bc261a45b
--- /dev/null
+++ b/packages/features/auth/lib/getServerSession.test.ts
@@ -0,0 +1,169 @@
+import type { NextApiRequest } from "next";
+import type { RequestMethod } from "node-mocks-http";
+import { createMocks } from "node-mocks-http";
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+// Use vi.hoisted to import mocks before vi.mock hoisting
+const {
+  prismaMock,
+  resetPrismaMock,
+  createLoggerMock,
+  createPrismaMock,
+  createLicenseKeyMock,
+  createDeploymentRepositoryMock,
+  createUserRepositoryMock,
+  createAvatarUrlMock,
+  createSafeStringifyMock,
+  createGetTokenMock,
+  createMockUser,
+  createMockToken,
+}: typeof import("../__mocks__/getServerSession.mocks") = await vi.hoisted(
+  async () => await import("../__mocks__/getServerSession.mocks")
+);
+
+vi.mock("@calcom/lib/logger", createLoggerMock);
+vi.mock("@calcom/prisma", createPrismaMock);
+vi.mock("@calcom/ee/common/server/LicenseKeyService", createLicenseKeyMock);
+vi.mock("@calcom/features/ee/deployment/repositories/DeploymentRepository", createDeploymentRepositoryMock);
+vi.mock("@calcom/features/users/repositories/UserRepository", createUserRepositoryMock);
+vi.mock("@calcom/lib/getAvatarUrl", createAvatarUrlMock);
+vi.mock("@calcom/lib/safeStringify", createSafeStringifyMock);
+vi.mock("next-auth/jwt", createGetTokenMock);
+
+import { getToken } from "next-auth/jwt";
+import { getServerSession } from "./getServerSession";
+
+type MockNextApiRequest = ReturnType<typeof createMocks<NextApiRequest>>["req"];
+
+function createMockRequest(method: RequestMethod = "GET"): MockNextApiRequest {
+  const { req } = createMocks<NextApiRequest>({ method });
+  return req;
+}
+
+function setupGetTokenMock(tokenData: object | null): void {
+  vi.mocked(getToken).mockResolvedValue(tokenData as Record<string, unknown> | null);
+}
+
+describe("getServerSession", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    resetPrismaMock();
+  });
+
+  describe("Token Validation", () => {
+    it.each([
+      ["no token", null],
+      ["no email", { sub: "5" }],
+      ["no sub", { email: "user@example.com" }],
+    ])("returns null when token is invalid: %s", async (_, token) => {
+      setupGetTokenMock(token);
+
+      const result = await getServerSession({ req: createMockRequest() });
+      expect(result).toBeNull();
+    });
+  });
+
+  describe("User ID Validation", () => {
+    it.each(["", "invalid", "0", "-1"])(
+      "returns null when token.sub is invalid (%s)",
+      async (sub) => {
+        setupGetTokenMock(createMockToken({ sub }));
+
+        const result = await getServerSession({ req: createMockRequest() });
+
+        expect(result).toBeNull();
+        expect(prismaMock.user.findUnique).not.toHaveBeenCalled();
+      }
+    );
+  });
+
+  describe("User Lookup", () => {
+    it("looks up user by ID from token.sub", async () => {
+      const mockUser = createMockUser({ id: 123 });
+      setupGetTokenMock(createMockToken({ sub: "123" }));
+      prismaMock.user.findUnique.mockResolvedValue(mockUser);
+
+      await getServerSession({ req: createMockRequest() });
+
+      expect(prismaMock.user.findUnique).toHaveBeenCalledWith({
+        where: { id: 123 },
+      });
+    });
+
+    it("returns null when user not found in database", async () => {
+      setupGetTokenMock(createMockToken({ sub: "999" }));
+      prismaMock.user.findUnique.mockResolvedValue(null);
+
+      const result = await getServerSession({ req: createMockRequest() });
+      expect(result).toBeNull();
+    });
+
+    it("returns session with correct user data", async () => {
+      const mockUser = createMockUser();
+      setupGetTokenMock(createMockToken());
+      prismaMock.user.findUnique.mockResolvedValue(mockUser);
+
+      const result = await getServerSession({ req: createMockRequest() });
+
+      expect(result).toMatchObject({
+        user: {
+          id: mockUser.id,
+          email: mockUser.email,
+        },
+      });
+    });
+  });
+
+  describe("User Resolution", () => {
+    it("resolves user by token subject ID", async () => {
+      const token = createMockToken({
+        sub: "999",
+        email: "user@example.com",
+      });
+
+      setupGetTokenMock(token);
+      prismaMock.user.findUnique.mockResolvedValue(null);
+
+      await getServerSession({ req: createMockRequest() });
+
+      expect(prismaMock.user.findUnique).toHaveBeenCalledWith({
+        where: { id: 999 },
+      });
+    });
+
+    it("returns user data from database lookup", async () => {
+      const dbUser = createMockUser({ id: 999, email: "db-user@example.com" });
+      const token = createMockToken({
+        sub: "999",
+        email: "token-email@example.com",
+      });
+
+      setupGetTokenMock(token);
+      prismaMock.user.findUnique.mockResolvedValue(dbUser);
+
+      const result = await getServerSession({ req: createMockRequest() });
+
+      expect(result).toMatchObject({
+        user: {
+          id: 999,
+          email: "db-user@example.com",
+        },
+      });
+    });
+
+    it("uses ID field for database queries", async () => {
+      const mockUser = createMockUser();
+      setupGetTokenMock(createMockToken());
+      prismaMock.user.findUnique.mockResolvedValue(mockUser);
+
+      await getServerSession({ req: createMockRequest() });
+
+      const calls = prismaMock.user.findUnique.mock.calls;
+      for (const call of calls) {
+        const whereClause = call[0]?.where as Record<string, unknown>;
+        expect(whereClause).toHaveProperty("id");
+        expect(whereClause).not.toHaveProperty("email");
+      }
+    });
+  });
+});
diff --git a/packages/features/auth/lib/getServerSession.ts b/packages/features/auth/lib/getServerSession.ts
index 5dc14368ea..1fab94ef10 100644
--- a/packages/features/auth/lib/getServerSession.ts
+++ b/packages/features/auth/lib/getServerSession.ts
@@ -54,10 +54,15 @@ export async function getServerSession(options: {
     return cachedSession;
   }
 
-  const email = token.email.toLowerCase();
+  const userId = token.sub ? Number(token.sub) : null;
+
+  if (!userId || userId <= 0) {
+    log.warn("Invalid or missing user ID in token", { sub: token.sub });
+    return null;
+  }
 
   const userFromDb = await prisma.user.findUnique({
-    where: { email },
+    where: { id: userId },
   });
 
   if (!userFromDb) {