diff --git a/backend/src/lib/authorization/ownership.ts b/backend/src/lib/authorization/ownership.ts
new file mode 100644
index 0000000..eb605b1
--- /dev/null
+++ b/backend/src/lib/authorization/ownership.ts
@@ -0,0 +1,19 @@
+import { eq, type AnyColumn } from "drizzle-orm";
+import { AppError } from "../errors";
+
+export function assertOwnsResource(
+  sessionUserId: string,
+  resourceUserId: string,
+  notFoundMessage = "Recurso não encontrado.",
+): void {
+  if (sessionUserId !== resourceUserId) {
+    throw AppError.notFound(notFoundMessage);
+  }
+}
+
+export function ownedBy<TUserIdColumn extends AnyColumn<{ data: string }>>(
+  userId: string,
+  userIdColumn: TUserIdColumn,
+) {
+  return eq(userIdColumn, userId);
+}
diff --git a/backend/src/modules/notifications/notifications.service.ts b/backend/src/modules/notifications/notifications.service.ts
index 14e67f1..ea713a3 100644
--- a/backend/src/modules/notifications/notifications.service.ts
+++ b/backend/src/modules/notifications/notifications.service.ts
@@ -2,6 +2,7 @@ import { and, count, desc, eq, isNull } from "drizzle-orm";
 import { db } from "../../db/client";
 import { NewUserNotification, SavedJob, userNotifications } from "../../db/schema";
 import { DB } from "../../db/types/types";
+import { ownedBy } from "../../lib/authorization/ownership";
 import { AppError } from "../../lib/errors";
 import {
   jobNotificationIdentity,
@@ -27,7 +28,7 @@ export class NotificationsService {
   constructor(private readonly tx: DB = db) {}
 
   async list(userId: string, filters: ListNotificationsQuery) {
-    const conditions = [eq(userNotifications.userId, userId)];
+    const conditions = [ownedBy(userId, userNotifications.userId)];
 
     if (filters.channel) {
       conditions.push(eq(userNotifications.channel, filters.channel));
@@ -50,7 +51,7 @@ export class NotificationsService {
         .from(userNotifications)
         .where(
           and(
-            eq(userNotifications.userId, userId),
+            ownedBy(userId, userNotifications.userId),
             filters.channel
               ? eq(userNotifications.channel, filters.channel)
               : undefined,
@@ -77,7 +78,7 @@ export class NotificationsService {
       .where(
         and(
           eq(userNotifications.id, notificationId),
-          eq(userNotifications.userId, userId),
+          ownedBy(userId, userNotifications.userId),
         ),
       )
       .returning();
@@ -95,7 +96,7 @@ export class NotificationsService {
       .set({ readAt: new Date() })
       .where(
         and(
-          eq(userNotifications.userId, userId),
+          ownedBy(userId, userNotifications.userId),
           channel ? eq(userNotifications.channel, channel) : undefined,
           isNull(userNotifications.readAt),
         ),
@@ -110,7 +111,7 @@ export class NotificationsService {
       .delete(userNotifications)
       .where(
         and(
-          eq(userNotifications.userId, userId),
+          ownedBy(userId, userNotifications.userId),
           channel ? eq(userNotifications.channel, channel) : undefined,
         ),
       )
@@ -181,7 +182,7 @@ export class NotificationsService {
     const existing = await this.tx.query.userNotifications.findFirst({
       where: (notification, { and, eq }) =>
         and(
-          eq(notification.userId, userId),
+          ownedBy(userId, notification.userId),
           eq(notification.type, "high_match"),
           eq(notification.entityType, "job"),
           eq(notification.entityId, entityId),
diff --git a/backend/src/modules/savedJobs/savedJobs.service.ts b/backend/src/modules/savedJobs/savedJobs.service.ts
index bbd27d9..eb08a1f 100644
--- a/backend/src/modules/savedJobs/savedJobs.service.ts
+++ b/backend/src/modules/savedJobs/savedJobs.service.ts
@@ -2,6 +2,7 @@ import { and, eq } from "drizzle-orm";
 import { db } from "../../db/client";
 import { NewSavedJob, SavedJob, savedJobs } from "../../db/schema";
 import { DB } from "../../db/types/types";
+import { ownedBy } from "../../lib/authorization/ownership";
 import { AppError } from "../../lib/errors";
 import { NotificationsService } from "../notifications/notifications.service";
 
@@ -10,14 +11,14 @@ export class SavedJobsService {
 
   async getAll(userId: string): Promise<SavedJob[]> {
     return this.tx.query.savedJobs.findMany({
-      where: (j, { eq }) => eq(j.userId, userId),
+      where: (j) => ownedBy(userId, j.userId),
       orderBy: (j, { desc }) => desc(j.createdAt),
     });
   }
 
   async getById(userId: string, jobId: string): Promise<SavedJob | undefined> {
     return this.tx.query.savedJobs.findFirst({
-      where: (j, { and, eq }) => and(eq(j.userId, userId), eq(j.id, jobId)),
+      where: (j, { and, eq }) => and(ownedBy(userId, j.userId), eq(j.id, jobId)),
     });
   }
 
@@ -27,7 +28,7 @@ export class SavedJobsService {
   ): Promise<SavedJob> {
     const existing = await this.tx.query.savedJobs.findFirst({
       where: (j, { and, eq }) =>
-        and(eq(j.userId, userId), eq(j.jobLink, data.jobLink)),
+        and(ownedBy(userId, j.userId), eq(j.jobLink, data.jobLink)),
     });
 
     if (existing) {
@@ -55,7 +56,7 @@ export class SavedJobsService {
     const result = await this.tx
       .update(savedJobs)
       .set({ ...data, updatedAt: new Date() })
-      .where(and(eq(savedJobs.id, jobId), eq(savedJobs.userId, userId)))
+      .where(and(eq(savedJobs.id, jobId), ownedBy(userId, savedJobs.userId)))
       .returning();
 
     if (!result[0]) {
@@ -72,6 +73,6 @@ export class SavedJobsService {
   async delete(userId: string, jobId: string): Promise<void> {
     await this.tx
       .delete(savedJobs)
-      .where(and(eq(savedJobs.id, jobId), eq(savedJobs.userId, userId)));
+      .where(and(eq(savedJobs.id, jobId), ownedBy(userId, savedJobs.userId)));
   }
 }
diff --git a/backend/src/modules/users/users.service.ts b/backend/src/modules/users/users.service.ts
index 67931de..e1c92f0 100644
--- a/backend/src/modules/users/users.service.ts
+++ b/backend/src/modules/users/users.service.ts
@@ -1,7 +1,7 @@
-import { eq } from "drizzle-orm";
 import { db } from "../../db/client";
 import { User, UserPreferences, userPreferences, users } from "../../db/schema";
 import { DB } from "../../db/types/types";
+import { ownedBy } from "../../lib/authorization/ownership";
 import { AppError } from "../../lib/errors";
 import { UpdateProfileData } from "../types/user.types";
 import { UpdatePreferencesData } from "./schemas/user.schemas";
@@ -30,7 +30,7 @@ export class UsersService {
 
   async getPreferences(userId: string): Promise<UserPreferences | undefined> {
     return this.tx.query.userPreferences.findFirst({
-      where: (p, { eq }) => eq(p.userId, userId),
+      where: (p) => ownedBy(userId, p.userId),
     });
   }
 
@@ -52,7 +52,7 @@ export class UsersService {
     const result = await this.tx
       .update(userPreferences)
       .set({ ...data, updatedAt: new Date() })
-      .where(eq(userPreferences.userId, userId))
+      .where(ownedBy(userId, userPreferences.userId))
       .returning();
 
     if (!result[0]) {
diff --git a/backend/src/routes/keywords.routes.ts b/backend/src/routes/keywords.routes.ts
index 4329586..5837df4 100644
--- a/backend/src/routes/keywords.routes.ts
+++ b/backend/src/routes/keywords.routes.ts
@@ -1,7 +1,7 @@
 import { Router } from "express";
-import { eq } from "drizzle-orm";
 import { db } from "../db/client";
 import { keywords } from "../db/schema";
+import { ownedBy } from "../lib/authorization/ownership";
 import { getCache } from "../lib/cache";
 import { publish } from "../lib/kwsync";
 
@@ -25,7 +25,7 @@ keywordsRoutes.get("/", async (req, res) => {
     const rows = await db
       .select({ keyword: keywords.keyword, source: keywords.source })
       .from(keywords)
-      .where(eq(keywords.userId, userId))
+      .where(ownedBy(userId, keywords.userId))
       .orderBy(keywords.createdAt);
 
     return res.json({ ok: true, keywords: rows });
diff --git a/backend/tests/unit/lib/authorization/ownership.test.ts b/backend/tests/unit/lib/authorization/ownership.test.ts
new file mode 100644
index 0000000..539527f
--- /dev/null
+++ b/backend/tests/unit/lib/authorization/ownership.test.ts
@@ -0,0 +1,43 @@
+import { describe, expect, it, vi } from "vitest";
+
+const mocks = vi.hoisted(() => ({
+  eq: vi.fn(),
+}));
+
+vi.mock("drizzle-orm", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("drizzle-orm")>();
+  return {
+    ...actual,
+    eq: mocks.eq,
+  };
+});
+
+import {
+  assertOwnsResource,
+  ownedBy,
+} from "../../../../src/lib/authorization/ownership";
+
+describe("ownership authorization helpers", () => {
+  it("permite recurso do usuário autenticado", () => {
+    expect(() => {
+      assertOwnsResource("user-1", "user-1", "Vaga");
+    }).not.toThrow();
+  });
+
+  it("retorna 404 quando o recurso pertence a outro usuário", () => {
+    expect(() => {
+      assertOwnsResource("user-1", "user-2", "Vaga não encontrada");
+    }).toThrow(expect.objectContaining({
+      code: "NOT_FOUND",
+      statusCode: 404,
+      message: "Vaga não encontrada",
+    }));
+  });
+
+  it("cria filtro Drizzle para userId", () => {
+    mocks.eq.mockReturnValue("owned-by-user-1");
+
+    expect(ownedBy("user-1", "user_id" as any)).toBe("owned-by-user-1");
+    expect(mocks.eq).toHaveBeenCalledWith("user_id", "user-1");
+  });
+});
diff --git a/backend/tests/unit/modules/notifications/notifications.service.test.ts b/backend/tests/unit/modules/notifications/notifications.service.test.ts
index 6649547..651d74d 100644
--- a/backend/tests/unit/modules/notifications/notifications.service.test.ts
+++ b/backend/tests/unit/modules/notifications/notifications.service.test.ts
@@ -1,4 +1,19 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const drizzleMocks = vi.hoisted(() => ({
+  and: vi.fn(),
+  eq: vi.fn(),
+}));
+
+vi.mock("drizzle-orm", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("drizzle-orm")>();
+  return {
+    ...actual,
+    and: drizzleMocks.and,
+    eq: drizzleMocks.eq,
+  };
+});
+
 import type {
   NewUserNotification,
   SavedJob,
@@ -94,6 +109,11 @@ describe("NotificationsService", () => {
   beforeEach(() => {
     tx = makeTx();
     service = new NotificationsService(tx as any);
+    drizzleMocks.and.mockImplementation((...conditions) => conditions);
+    drizzleMocks.eq.mockImplementation((column, value) => ({
+      column,
+      value,
+    }));
   });
 
   it("lista notificações com filtros de canal e não lidas", async () => {
@@ -113,6 +133,11 @@ describe("NotificationsService", () => {
     });
     expect(listBuilder.limit).toHaveBeenCalledWith(10);
     expect(tx.select).toHaveBeenCalledTimes(2);
+    expect(listBuilder.where).toHaveBeenCalledWith(
+      expect.arrayContaining([
+        { column: expect.anything(), value: "user-1" },
+      ]),
+    );
   });
 
   it("usa unreadCount zero quando a consulta agregada não retorna linhas", async () => {
@@ -155,6 +180,10 @@ describe("NotificationsService", () => {
       service.markRead("user-1", "notification-1"),
     ).resolves.toBe(notification);
     expect(update.set).toHaveBeenCalledWith({ readAt: expect.any(Date) });
+    expect(update.where).toHaveBeenCalledWith([
+      { column: expect.anything(), value: "notification-1" },
+      { column: expect.anything(), value: "user-1" },
+    ]);
   });
 
   it("lança not found ao marcar como lida quando não encontra a notificação", async () => {
@@ -176,6 +205,12 @@ describe("NotificationsService", () => {
     await expect(service.markAllRead("user-1", "message")).resolves.toEqual({
       updated: 2,
     });
+    expect(update.where).toHaveBeenCalledWith(
+      expect.arrayContaining([
+        { column: expect.anything(), value: "user-1" },
+        { column: expect.anything(), value: "message" },
+      ]),
+    );
   });
 
   it("limpa notificações de um canal", async () => {
@@ -187,6 +222,12 @@ describe("NotificationsService", () => {
     });
 
     expect(tx.delete).toHaveBeenCalled();
+    expect(deleteQuery.where).toHaveBeenCalledWith(
+      expect.arrayContaining([
+        { column: expect.anything(), value: "user-1" },
+        { column: expect.anything(), value: "notification" },
+      ]),
+    );
     expect(deleteQuery.returning).toHaveBeenCalledWith({
       id: expect.anything(),
     });
@@ -326,4 +367,32 @@ describe("NotificationsService", () => {
       }),
     );
   });
+
+  it("deduplica alto match usando userId para impedir colisão cross-user", async () => {
+    tx.query.userNotifications.findFirst.mockResolvedValue(notification);
+
+    const result = await service.createHighMatchIfMissing("user-1", {
+      id: "job-1",
+      title: "Backend Developer",
+      company: "Candidate",
+      link: "https://jobs.test/1",
+      matchScore: 95,
+    });
+
+    expect(result).toBe(notification);
+
+    const where = tx.query.userNotifications.findFirst.mock.calls[0][0].where;
+    const table = {
+      userId: "userNotifications.userId",
+      type: "userNotifications.type",
+      entityType: "userNotifications.entityType",
+      entityId: "userNotifications.entityId",
+    };
+    expect(where(table, drizzleMocks)).toEqual([
+      { column: "userNotifications.userId", value: "user-1" },
+      { column: "userNotifications.type", value: "high_match" },
+      { column: "userNotifications.entityType", value: "job" },
+      { column: "userNotifications.entityId", value: "job-1" },
+    ]);
+  });
 });
diff --git a/backend/tests/unit/modules/savedJobs/savedJobs.service.test.ts b/backend/tests/unit/modules/savedJobs/savedJobs.service.test.ts
index dfa5913..8247dc4 100644
--- a/backend/tests/unit/modules/savedJobs/savedJobs.service.test.ts
+++ b/backend/tests/unit/modules/savedJobs/savedJobs.service.test.ts
@@ -1,5 +1,19 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
 
+const drizzleMocks = vi.hoisted(() => ({
+  and: vi.fn(),
+  eq: vi.fn(),
+}));
+
+vi.mock("drizzle-orm", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("drizzle-orm")>();
+  return {
+    ...actual,
+    and: drizzleMocks.and,
+    eq: drizzleMocks.eq,
+  };
+});
+
 // ─── Fixtures ─────────────────────────────────────────────────────────────────
 
 const mockJob = {
@@ -42,6 +56,11 @@ describe("SavedJobsService", () => {
   beforeEach(() => {
     tx = makeMockTx();
     service = new SavedJobsService(tx as any);
+    drizzleMocks.and.mockImplementation((...conditions) => conditions);
+    drizzleMocks.eq.mockImplementation((column, value) => ({
+      column,
+      value,
+    }));
   });
 
   // ── getAll ─────────────────────────────────────────────────────────────────
@@ -76,6 +95,19 @@ describe("SavedJobsService", () => {
       expect(result).toEqual(mockJob);
     });
 
+    it("monta filtro com jobId e userId para impedir leitura cross-user", async () => {
+      tx.query.savedJobs.findFirst.mockResolvedValue(mockJob);
+
+      await service.getById("user-1", "job-1");
+
+      const where = tx.query.savedJobs.findFirst.mock.calls[0][0].where;
+      const table = { userId: "savedJobs.userId", id: "savedJobs.id" };
+      expect(where(table, drizzleMocks)).toEqual([
+        { column: "savedJobs.userId", value: "user-1" },
+        { column: "savedJobs.id", value: "job-1" },
+      ]);
+    });
+
     it("retorna undefined quando vaga não existe", async () => {
       tx.query.savedJobs.findFirst.mockResolvedValue(undefined);
 
@@ -137,6 +169,32 @@ describe("SavedJobsService", () => {
 
       expect(tx.insert).not.toHaveBeenCalled();
     });
+
+    it("verifica duplicidade por jobLink apenas dentro do mesmo usuário", async () => {
+      tx.query.savedJobs.findFirst.mockResolvedValue(undefined);
+      tx.insert.mockReturnValueOnce({
+        values: vi.fn().mockReturnValue({
+          returning: vi.fn().mockResolvedValue([{ ...mockJob, ...newJobData }]),
+        }),
+      });
+      tx.insert.mockReturnValueOnce({
+        values: vi.fn().mockReturnValue({
+          returning: vi.fn().mockResolvedValue([{ id: "notification-1" }]),
+        }),
+      });
+
+      await service.create("user-1", newJobData);
+
+      const where = tx.query.savedJobs.findFirst.mock.calls[0][0].where;
+      const table = {
+        userId: "savedJobs.userId",
+        jobLink: "savedJobs.jobLink",
+      };
+      expect(where(table, drizzleMocks)).toEqual([
+        { column: "savedJobs.userId", value: "user-1" },
+        { column: "savedJobs.jobLink", value: newJobData.jobLink },
+      ]);
+    });
   });
 
   // ── update ─────────────────────────────────────────────────────────────────
@@ -202,6 +260,23 @@ describe("SavedJobsService", () => {
       expect(setArg.updatedAt).toBeInstanceOf(Date);
     });
 
+    it("atualiza usando jobId e userId para impedir alteração cross-user", async () => {
+      const whereMock = vi.fn().mockReturnValue({
+        returning: vi.fn().mockResolvedValue([mockJob]),
+      });
+      tx.query.savedJobs.findFirst.mockResolvedValue(mockJob);
+      tx.update.mockReturnValue({
+        set: vi.fn().mockReturnValue({ where: whereMock }),
+      });
+
+      await service.update("user-1", "job-1", { jobTitle: "X" });
+
+      expect(whereMock).toHaveBeenCalledWith([
+        { column: expect.anything(), value: "job-1" },
+        { column: expect.anything(), value: "user-1" },
+      ]);
+    });
+
     it("cria notificação quando o status da vaga muda", async () => {
       const previousJob = { ...mockJob, status: "saved" };
       const updatedJob = { ...mockJob, status: "applied" };
@@ -252,5 +327,17 @@ describe("SavedJobsService", () => {
       await expect(service.delete("user-1", "job-1")).resolves.toBeUndefined();
       expect(tx.delete).toHaveBeenCalledOnce();
     });
+
+    it("deleta usando jobId e userId para impedir remoção cross-user", async () => {
+      const whereMock = vi.fn().mockResolvedValue(undefined);
+      tx.delete.mockReturnValue({ where: whereMock });
+
+      await service.delete("user-1", "job-1");
+
+      expect(whereMock).toHaveBeenCalledWith([
+        { column: expect.anything(), value: "job-1" },
+        { column: expect.anything(), value: "user-1" },
+      ]);
+    });
   });
 });