Hoverfly is an open source API simulation tool. In versions 1.11.3 and prior, the middleware functionality in Hoverfly is vulnerable to command injection vulnerability at `/api/v2/hoverfly/middleware` endpoint due to insufficient validation and sanitization in user input. The vulnerability exists in the middleware management API endpoint `/api/v2/hoverfly/middleware`. This issue is born due to combination of three code level flaws: Insufficient Input Validation in middleware.go line 94-96; Unsafe Command Execution in local_middleware.go line 14-19; and Immediate Execution During Testing in hoverfly_service.go line 173. This allows an attacker to gain remote code execution (RCE) on any system running the vulnerable Hoverfly service. Since the input is directly passed to system commands without proper checks, an attacker can upload a malicious payload or directly execute arbitrary commands (including reverse shells) on the host server with the privileges of the Hoverfly process. Commit 17e60a9bc78826deb4b782dca1c1abd3dbe60d40 in version 1.12.0 disables the set middleware API by default, and subsequent changes to documentation make users aware of the security changes of exposing the set middleware API.

Affected: Go: github.com/SpectoLabs/hoverfly

### Summary It has been discovered that the middleware functionality in Hoverfly is vulnerable to command injection through its `/api/v2/hoverfly/middleware` endpoint due to insufficient validation and sanitization in user input.

### Details The vulnerability exists in the middleware management API endpoint `/api/v2/hoverfly/middleware`.

This issue is born due to combination of three code level flaws:

1. Insufficient Input Validation in [middleware.go line 94-96](https://github.com/SpectoLabs/hoverfly/blob/master/core/middleware/middleware.go#L93):

``` func (this *Middleware) SetBinary(binary string) error { this.Binary = binary // No validation of binary parameter here return nil } ```

2. Unsafe Command Execution in [local_middleware.go line 14-19](https://github.com/SpectoLabs/hoverfly/blob/master/core/middleware/local_middleware.go#L13):

``` var middlewareCommand *exec.Cmd if this.Script == nil { middlewareCommand = exec.Command(this.Binary) // User-controlled binary } else { middlewareCommand = exec.Command(this.Binary, this.Script.Name()) // User-controlled binary and script } ```

3. Immediate Execution During Testing in [hoverfly_service.go line 173](https://github.com/SpectoLabs/hoverfly/blob/master/core/hoverfly_service.go#L173):

``` _, err = newMiddleware.Execute(testData) // Executes middleware immediately for testing ```

### POC

1. Send the below HTTP PUT request to `http://localhost:8888` in order to create our malicious middleware,…

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