Impact

A PHP Object Injection vulnerability affects the PrestaShop module ps_facetedsearch.

The module rebuilds the selected search filters from the request URL. The value of a slider filter (price or weight) is taken from the URL without sufficient validation, then stored in an internal filter-block cache where it is serialized and later read back with a raw native unserialize().
By crafting that value, an attacker can smuggle a malicious serialized PHP object into the cache. When it is deserialized, a gadget chain writes an arbitrary PHP file inside the module directory, which is then used as a webshell to run commands on the server.

Who is impacted

Any shop using a vulnerable version of ps_facetedsearch that displays a filter template containing a slider filter (price or weight). Exploitation is remote and unauthenticated, a single crafted front-office request is enough, and leads to remote code
execution and full compromise of the shop and its server.

Affected versions: 3.0.0 through 4.0.3 (all versions since 3.0.0, including the latest release).

Patches

Upgrade the ps_facetedsearch module to the patched version. Upgrading the module is the best action that removes the vulnerability.

Otherwise, you can apply the fix manually in the file src/Filters/Block.php:

In the getFromCache() method, replace the native unserialize() call:

// Before
if (!empty($row)) {
    return unserialize(current($row));
}

// After
if (!empty($row)) {
    return \Tools::unSerialize(current($row));
}

Until the module is upgraded:

• Remove price and weight slider filters from the filter templates that are exposed on the
  front office.
• Clear the faceted-search filter cache, and audit the modules/ps_facetedsearch/ directory for
  unexpected PHP files.
• Monitor search requests for PHP serialization patterns (O:, ;i:, references to classes such
  as Monolog\…) and block them at the WAF level.

Resources

• Thank you to Frédéric Moreau (Antadis) and Gilles Caudal (Datalinx) for reporting this vulnerability.

References

• GHSA-m5f5-28qr-9g9r