Tautulli vulnerable to Authenticated Remote Code Execution via Command Injection

Tautulli is a Python based monitoring and tracking tool for Plex Media Server. A command injection vulnerability in Tautulli v2.15.3 and prior allows attackers with administrative privileges to obtain remote code execution on the application server. This vulnerability requires the application to have been cloned from GitHub and installed manually. When Tautulli is cloned directly from GitHub and installed manually, the application manages updates and versioning through calls to the `git` command. In the code, this is performed through the `runGit` function in `versioncheck.py`. Since `shell=True` is passed to `subproces.Popen`, this call is vulnerable to subject to command injection, as shell characters within arguments will be passed to the underlying shell. A concrete location where this can be triggered is in the `checkout_git_branch` endpoint. This endpoint stores a user-supplied remote and branch name into the `GIT_REMOTE` and `GIT_BRANCH` configuration keys without sanitization. Downstream, these keys are then fetched and passed directly into `runGit` using a format string. Hence, code execution can be obtained by using `$()` interpolation in a command. Version 2.16.0 contains a fix for the issue.