Vue.js 2 Vee-validate (pt-br) CPF Validation

app.js

// The Vue build version to load with the `import` command
// (runtime-only or standalone) has been set in webpack.base.conf with an alias.
import Vue from 'vue'
import App from './App'
import VeeValidator, { Validator } from 'vee-validate'
import CpfValidator from './components/validators/cpf.validator'
import Dictionary from './components/validators/dictionary'
import Produto from './components/produtos.vue'

Validator.extend('cpf', CpfValidator)

Vue.use(VeeValidator, {locale: 'pt', dictionary: Dictionary})
Vue.config.debug = true
/* eslint-disable no-new */
Vue.component('produtos', Produto)
new Vue({
  el: '#app',
  render: h => h(App)
})

cpf.js

function calcChecker1 (firstNineDigits) {
  let sum = null

  for (let j = 0; j < 9; ++j) {
    sum += firstNineDigits.toString().charAt(j) * (10 - j)
  }

  const lastSumChecker1 = sum % 11
  const checker1 = (lastSumChecker1 < 2) ? 0 : 11 - lastSumChecker1

  return checker1
}

function calcChecker2 (cpfWithChecker1) {
  let sum = null

  for (let k = 0; k < 10; ++k) {
    sum += cpfWithChecker1.toString().charAt(k) * (11 - k)
  }
  const lastSumChecker2 = sum % 11
  const checker2 = (lastSumChecker2 < 2) ? 0 : 11 - lastSumChecker2

  return checker2
}

function cleaner (value) {
  const digits = value.replace(/[^\d]/g, '')
  return digits
}

function validate (value) {
  const cleanCPF = cleaner(value)
  const firstNineDigits = cleanCPF.substring(0, 9)
  const checker = cleanCPF.substring(9, 11)
  let result = false

  for (let i = 0; i < 10; i++) {
    if (firstNineDigits + checker === Array(12).join(i)) {
      return false
    }
  }

  const checker1 = calcChecker1(firstNineDigits)
  const checker2 = calcChecker2(`${firstNineDigits}${checker1}`)

  if (checker.toString() === checker1.toString() + checker2.toString()) {
    result = true
  } else {
    result = false
  }
  return result
}
export default validate

cpf.validator.js

import CpfValidate from './rules/cpf'
const validator = {
  getMessage (field, args) { // will be added to default English messages.
    return 'Invalid CPF'
  },
  validate (value, args) {
    return CpfValidate(value)
  }
}
export default validator

dictionary.js

const dictionary = {
  pt: {
    messages: {
      cpf: () => 'CPF inválido',
      required: (field) => `O campo ${field} é obrigatório.`
    }
  }
}
export default dictionary

@daasc, cheguei um pouco tarde, mas é assim (VeeValidate 3.x):

<ValidationProvider rules="required|cpf" v-slot="{ errors }">
  <input
    id="cardHolderCPF"
    type="text"
    name="cpf"
    v-model="cardHolderCPF"
    v-mask="'###.###.###-##'"
    placeholder="___.___.___-__"
    class="input focus:outline-none focus:shadow mb-2"
    :class="{'border-red-500 error': errors.length > 0}"
    autocomplete="cpf"
    required
  />
  <p class="text-red-500 text-xs italic" v-show="errors.length > 0">{{ errors[0] }}</p>
</ValidationProvider>