ps_facetedsearch: PHP Object Injection in faceted search cache allows unauthenticated RCE

PrestaShop ps_facetedsearch is a module that adds layered navigation filters. From 3.0.0 until 4.0.4, the ps_facetedsearch module rebuilds selected search filters from the request URL, and the value of a slider filter, price or weight, is taken from the URL without sufficient validation and stored in an internal filter-block cache where it is serialized and later read back with a raw native unserialize() in src/Filters/Block.php. By crafting that value, an unauthenticated attacker can smuggle a malicious serialized PHP object into the cache, and when it is deserialized, a gadget chain writes an arbitrary PHP file inside the modules/ps_facetedsearch/ directory, which is then used as a webshell to run commands on the server. This issue is fixed in version 4.0.4.