fix: reject remote-helper git flags that enable RCE

README.md

@@ -101,6 +101,9 @@ Add a step like this to your workflow:
 Multiple options let you provide the `git` arguments that you want the action to use. It's important to note that these arguments **are not actually used with a CLI command**, but they are parsed by a package called [`string-argv`](https://npm.im/string-argv), and then used with [`simple-git`](https://npm.im/simple-git).  
 What does this mean for you? It means that strings that contain a lot of nested quotes may be parsed incorrectly, and that specific ways of declaring arguments may not be supported by these libraries. If you're having issues with your argument strings you can check whether they're being parsed correctly either by [enabling debug logging](https://docs.github.com/en/actions/managing-workflow-runs/enabling-debug-logging) for your workflow runs or by testing it directly with `string-argv` ([RunKit demo](https://npm.runkit.com/string-argv)): if each argument and option is parsed correctly you'll see an array where every string is an option or value.
 
+Remote-helper overrides (`--upload-pack`, `--receive-pack`, `--exec`, and abbreviations of those) are rejected: they can make git run an arbitrary local program during fetch/pull/push.  
+Do not interpolate untrusted data (for example values from `github.event.*`) into `fetch`, `pull`, `push`, or `tag_push` without sanitizing them first.
+
 ### Adding files
 
 The action adds files using a regular `git add` command, so you can put every kind of argument in the `add` option. For example, if you want to force-add a file: `./path/to/file.txt --force`.