An issue was discovered in Deskpro before 2019.8.0. This product enables administrators to modify the helpdesk interface by editing /portal/api/style/edit-theme-set/template-sources theme templates, and uses TWIG as its template engine. While direct access to self and _self variables was not permitted, one could abuse the accessible variables in ones context to reach a native unserialize function via the code parameter. There, on could pass a crafted payload to trigger a set of POP gadgets in order to achieve remote code execution.
The product deserializes untrusted data without sufficiently verifying that the resulting data will be valid.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Deskpro | Deskpro | * | 2019.8.0 (excluding) |
It is often convenient to serialize objects for communication or to save them for later use. However, deserialized data or code can often be modified without using the provided accessor functions if it does not use cryptography to protect itself. Furthermore, any cryptography would still be client-side security – which is a dangerous security assumption. Data that is untrusted can not be trusted to be well-formed. When developers place no restrictions on “gadget chains,” or series of instances and method invocations that can self-execute during the deserialization process (i.e., before the object is returned to the caller), it is sometimes possible for attackers to leverage them to perform unauthorized actions, like generating a shell.