fix(users): never manage or hand out more than the caller holds

A role with users:update could reset an administrator's password or MFA,
change the admin's email to one it controls, or give a colluding account
the ADMIN role (with users:assign-role) - and so become administrator.

Every management action (update, deactivate, activate, reset password,
reset MFA) and every role assignment now requires the target role's grants
to be a subset of the caller's own, like role editing already did. The
target role is read from its grants, so a deactivated admin still counts
as an admin. Changing another user's email revokes their sessions.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/src/users/users.service.ts

@@ -78,6 +78,38 @@ export class UsersService {
     }
   }
 
+  /**
+   * Nobody may act on - or hand out - more than they can do themselves: a
+   * limited "user manager" holding users:update could otherwise reset an
+   * administrator's password or MFA, change their email to one they control,
+   * or give a colluding account the ADMIN role, and so become admin. Same
+   * rule as RolesService.assertCanGrantPermissions. Reads the role's grants
+   * directly (not the cached effective set), so a deactivated admin counts
+   * as an admin too.
+   */
+  private async assertWithinCallerPermissions(
+    roleId: string,
+    actingUserId?: string,
+  ): Promise<void> {
+    if (!actingUserId) {
+      return;
+    }
+    const grants = await this.prisma.rolePermission.findMany({
+      where: { roleId },
+      select: { permission: { select: { key: true } } },
+    });
+    const callerPermissions =
+      await this.permissionResolver.getPermissions(actingUserId);
+    const exceeds = grants.some(
+      (grant) => !callerPermissions.has(grant.permission.key),
+    );
+    if (exceeds) {
+      throw new ForbiddenException(
+        'Dieses Konto hat mehr Rechte als Sie selbst und kann von Ihnen nicht verwaltet werden',
+      );
+    }
+  }
+
   private async assertActiveRole(roleId: string): Promise<void> {
     const role = await this.prisma.role.findUnique({ where: { id: roleId } });
     if (!role) {
@@ -151,6 +183,7 @@ export class UsersService {
     }
     await this.assertActiveRole(dto.roleId);
     await this.assertCanAssignRole(actingUserId);
+    await this.assertWithinCallerPermissions(dto.roleId, actingUserId);
     const passwordHash = await bcrypt.hash(dto.password, BCRYPT_SALT_ROUNDS);
     const user = await this.prisma.user.create({
       data: {
@@ -177,7 +210,9 @@ export class UsersService {
     actingUserId?: string,
   ): Promise<UserSummary> {
     const before = await this.findById(id);
+    await this.assertWithinCallerPermissions(before.roleId, actingUserId);
     const roleChanged = Boolean(dto.roleId) && dto.roleId !== before.roleId;
+    const emailChanged = dto.email !== undefined && dto.email !== before.email;
     if (dto.roleId) {
       await this.assertActiveRole(dto.roleId);
     }
@@ -189,6 +224,7 @@ export class UsersService {
         throw new ForbiddenException('Cannot change your own role');
       }
       await this.assertCanAssignRole(actingUserId);
+      await this.assertWithinCallerPermissions(dto.roleId!, actingUserId);
       await this.assertNotLastSystemRoleUser(id);
     }
     const user = await this.prisma.user.update({
@@ -200,7 +236,15 @@ export class UsersService {
       },
       ...USER_WITH_ROLE,
     });
-    if (roleChanged) {
+    if (emailChanged) {
+      // The email is the login name and the SSO link: sessions opened under
+      // the old one end here.
+      await this.prisma.refreshToken.updateMany({
+        where: { userId: id, revokedAt: null },
+        data: { revokedAt: new Date() },
+      });
+    }
+    if (roleChanged || emailChanged) {
       this.permissionResolver.invalidateUser(id);
     }
     await this.auditLog.record({
@@ -216,6 +260,7 @@ export class UsersService {
 
   async deactivate(id: string, actingUserId?: string): Promise<UserSummary> {
     const before = await this.findById(id);
+    await this.assertWithinCallerPermissions(before.roleId, actingUserId);
     await this.assertNotLastSystemRoleUser(id);
     const user = await this.prisma.user.update({
       where: { id },
@@ -262,7 +307,8 @@ export class UsersService {
         'Use /profile/password to change your own password',
       );
     }
-    await this.findById(id);
+    const target = await this.findById(id);
+    await this.assertWithinCallerPermissions(target.roleId, actingUserId);
     const passwordHash = await bcrypt.hash(dto.password, BCRYPT_SALT_ROUNDS);
     const user = await this.prisma.user.update({
       where: { id },
@@ -291,7 +337,8 @@ export class UsersService {
         'Use /profile/mfa/disable to disable your own MFA',
       );
     }
-    await this.findById(id);
+    const target = await this.findById(id);
+    await this.assertWithinCallerPermissions(target.roleId, actingUserId);
     const user = await this.prisma.user.update({
       where: { id },
       data: { mfaEnabled: false, mfaSecret: null },
@@ -308,6 +355,7 @@ export class UsersService {
 
   async activate(id: string, actingUserId?: string): Promise<UserSummary> {
     const before = await this.findById(id);
+    await this.assertWithinCallerPermissions(before.roleId, actingUserId);
     if (before.isActive) {
       throw new ConflictException('User is already active');
     }