FreeScout's deserialization of untrusted data can lead to Remote Code Execution

Vulnerability Description

FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. Versions 1.8.185 and earlier contain a deserialization of untrusted data vulnerability that allows authenticated attackers with knowledge of the application's APP_KEY to achieve remote code execution. The vulnerability is exploited via endpoint, e.g.: `/help/{mailbox_id}/auth/{customer_id}/{hash}/{timestamp}` where the `customer_id` and `timestamp` parameters are processed through the decrypt function in `app/Helper.php` without proper validation. The code decrypts using Laravel's built-in encryption functions, which subsequently deserialize the decrypted payload without sanitization, allowing attackers to craft malicious serialized PHP objects using classes to trigger arbitrary command execution. This is fixed in version 1.8.186.

References

• https://github.com/freescout-help-desk/freescout/security/advisories/GHSA-j94w-q9gj-c37g
• https://github.com/freescout-help-desk/freescout/commit/e2de65f3f32f825b4ec5558643ed81438c9a6bc6
• https://github.com/freescout-help-desk/freescout/releases/tag/1.8.186