Tremor is an event processing system for unstructured data. A vulnerability exists between versions 0.7.2 and 0.11.6. This vulnerability is a memory safety Issue when using `patch` or `merge` on `state` and assign the result back to `state`. In this case, affected versions of Tremor and the tremor-script crate maintains references to memory that might have been freed already. And these memory regions can be accessed by retrieving the `state`, e.g. send it over TCP or HTTP. This requires the Tremor server (or any other program using tremor-script) to execute a tremor-script script that uses the mentioned language construct. The issue has been patched in version 0.11.6 by removing the optimization and always cloning the target expression of a Merge or Patch. If an upgrade is not possible, a possible workaround is to avoid the optimization by introducing a temporary variable and not immediately reassigning to `state`.

Affected: crates.io: tremor-script

### Impact

This vulnerability is a memory safety Issue when using [`patch`](https://www.tremor.rs/docs/tremor-script/index#patch) or [`merge`](https://www.tremor.rs/docs/tremor-script/index#merge) on `state` and assign the result back to `state`. In this case affected versions of Tremor and the [tremor-script crate](https://crates.io/crates/tremor-script) maintains references to memory that might have been freed already. And these memory regions can be accessed by retrieving the `state`, e.g. send it over TCP or HTTP. This requires the Tremor server (or any other program using tremor-script) to execute a tremor-script script that uses the mentioned language construct.

#### Details

If affects the following two tremor-script language constructs:

* A [Merge](https://www.tremor.rs/docs/tremor-script/index#merge) where we assign the result back to the target expression and the expression to be merged needs to reference the `event`:

``` let state = merge state of event end; ```

* A [Patch](https://www.tremor.rs/docs/tremor-script/index#patch) where we assign the result back to the target expression and the patch operations used need to reference the `event`:

``` let state = patch state of insert event.key => event.value end; ```

For constructs like this (it does not matter what it references in the expression to be merged or the patch operations) an optimization was applied to manipulate the target value in-place, instead of cloning it.

Our `Value` struct, which under…