GitHub Actions nx can let attacker run commands

## Summary

Nx core builds several `git` invocations as shell command strings with untrusted values interpolated into them, so a value that should be a git revision or ref is parsed by `/bin/sh` instead. Two entry points are reachable by an attacker: `affected` commands, where `defaultBase` / `affected.defaultBase` from `nx.json` (and the `NX_BASE` / `NX_HEAD` environment variables) reach `git merge-base` and `git diff`; and `nx import`, where a branch name advertised by a remote repository reaches `git fetch`, `git checkout`, and `git config`. In both cases an attacker who controls a repository — or who opens a pull request against one — gets arbitrary command execution on the machine of anyone who runs an ordinary Nx command against it, including CI runners.

The `affected` path is the more serious of the two. `nx affected` and `nx show projects --affected` run constantly in CI, so a pull request that changes nothing but `nx.json` is enough to execute code on the runner with whatever credentials that job holds.

## Severity

Exploitable by anyone who controls repository content — a fork's pull request, or a repository the victim clones — that the victim then runs an ordinary `nx affected` or `nx import` against; no access to the victim's machine is required. We have no evidence of exploitation in the wild.

## Affected & Patched Versions

| Package | Vulnerable | Patched |
| --- | --- | --- |
| `nx` | `>= 14.0.0, < 22.7.8`; `>= 23.0.0, < 23.1.1` | `22.7.8`, `23.1.1` |

Treat every version below the patched ones as affected.

## Remediation

Upgrade to **22.7.8** (22.x line) or **23.1.1** (23.x line) or later:

```
nx migrate 23.1.1
```

The fix is a drop-in — no configuration changes are required. If you cannot upgrade, treat `nx.json` from untrusted sources as executable content, do not run `affected` commands against pull requests you have not reviewed, and do not run `nx import` against repositories you do not trust.

## Details

### `affected` commands

Nx computes the merge base and the changed-file set by building `git merge-base` and `git diff` command lines as strings and running them through a shell. The base and head revisions in those strings come from `nx.json`'s `defaultBase` / `affected.defaultBase` or from the `NX_BASE` / `NX_HEAD` environment variables, and a related code path reads file contents with `git show <revision>:<path>` the same way. Because a shell parses the whole line, a revision value containing shell syntax is executed rather than passed to `git`.

The revisions are wrapped in double quotes, which looks protective but is not: POSIX shells still perform command substitution inside double quotes, so a value of `$(…)` runs without needing to break out of the quotes.

### `nx import`

The `GitRepository` helper runs every git operation — `fetch`, `checkout`, `reset`, `config`, and others — by interpolating its arguments into a shell command string. The untrusted argument is a branch name: `nx import` lists the branches a remote advertises, offers them to the user to choose from, and feeds the chosen name back into those commands. A hostile repository controls the names of its own branches, so it controls the command that runs when one is selected.


## Credits

- **Arkadiusz Marta** (RE:SOURCE) — Reporter