Pimcore has Unsafe PHP Deserialization in Multiple Locations Without allowed_classes Restriction

# GM-374

Summary

Multiple locations in Pimcore v11 call PHP's unserialize() on data from database columns and filesystem files without the allowed_classes restriction, enabling object injection if an attacker can control the serialized data source.

Affected

Component - Package: pimcore/pimcore and pimcore/admin-ui-classic-bundle - Files: - lib/Tool/Authentication.php (line 82) — session token deserialization - models/Site/Dao.php (line 68) — site domains from database - models/DataObject/ClassDefinition/CustomLayout/Dao.php (line 69) — layout definitions from database - models/Tool/TmpStore/Dao.php (line 64) — temporary store data from database - models/Asset/WebDAV/Service.php (line 36) — delete log from filesystem - admin-ui-classic-bundle/src/Helper/Dashboard.php (line 64) — dashboard config from filesystem

Description

Six locations in Pimcore core call unserialize() directly (bypassing Tool\Serialize) on data sourced from database columns or filesystem files without passing the allowed_classes parameter. This means any class available in the autoloader will be instantiated during deserialization.

If an attacker can write to the data source (e.g., via SQL injection targeting the tmp_store, sites, or custom_layouts tables, or via a file write vulnerability targeting the WebDAV delete log), they can inject serialized PHP gadget chains that execute arbitrary code when the data is deserialized.

This is related to but distinct from the Tool\Serialize::unserialize() issue — these calls bypass the wrapper entirely.

Impact

PHP object injection leading to Remote Code Execution when chained with a data source write vulnerability. Pimcore's dependency tree (Guzzle, Symfony, Monolog, Doctrine) provides numerous known gadget chains.

Proof of

Concept 1. Identify a writable data source (e.g., tmp_store table via SQL injection, or webdav-delete.dat via file write) 2. Write a serialized PHP gadget chain (e.g., Monolog BufferHandler chain from phpggc) 3. Trigger the deserialization (e.g., access a page that reads TmpStore, or trigger a WebDAV operation) 4. The gadget chain executes with web server privileges

Suggested

Fix Add allowed_classes parameter to all unserialize() calls. Where no objects are needed, use ['allowed_classes' => false]. Consider migrating to JSON serialization for data that doesn't require object preservation.

// Example fix for Site/Dao.php:
$siteDomains = unserialize($site['domains'], ['allowed_classes' => false]);

// Example fix for TmpStore/Dao.php:
$item['data'] = unserialize($item['data'], ['allowed_classes' => false]);

## Resources - CWE-502: Deserialization of Untrusted Data - OWASP Deserialization Cheat Sheet - phpggc: PHP Generic Gadget Chains