CVE-2021-32724 check-spelling workflow vulnerable to GITHUB_TOKEN leakage via symlink attack
Attackers can leak GITHUB_TOKEN via symlink attacks in check-spelling workflows, enabling repository write access and secret theft.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-32724?
CVE-2021-32724 is a critical vulnerability in check-spelling, published on 9 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
check-spelling is a github action which provides CI spell checking. In affected versions and for a repository with the [check-spelling action](https://github.com/marketplace/actions/check-spelling) enabled that triggers on `pull_request_target` (or `schedule`), an attacker can send a crafted Pull Request that causes a `GITHUB_TOKEN` to be exposed. With the `GITHUB_TOKEN`, it's possible to push commits to the repository bypassing standard approval processes. Commits to the repository could then steal any/all secrets available to the repository. As a workaround users may can either: [Disable the workflow](https://docs.github.com/en/actions/managing-workflow-runs/disabling-and-enabling-a-workflow) until you've fixed all branches or Set repository to [Allow specific actions](https://docs.github.com/en/github/administering-a-repository/managing-repository-settings/disabling-or-limiting-github-actions-for-a-repository#allowing-specific-actions-to-run). check-spelling isn't a verified creator and it certainly won't be anytime soon. You could then explicitly add other actions that your repository uses. Set repository [Workflow permissions](https://docs.github.com/en/github/administering-a-repository/managing-repository-settings/disabling-or-limiting-github-actions-for-a-repository#setting-the-permissions-of-the-github_token-for-your-repository) to `Read repository contents permission`. Workflows using `check-spelling/check-spelling@main` will get the fix automatically. Workflows using a pinned sha or tagged version will need to change the affected workflows for all repository branches to the latest version. Users can verify who and which Pull Requests have been running the action by looking up the spelling.yml action in the Actions tab of their repositories, e.g., https://github.com/check-spelling/check-spelling/actions/workflows/spelling.yml - you can filter PRs by adding ?query=event%3Apull_request_target, e.g., https://github.com/check-spelling/check-spelling/actions/workflows/spelling.yml?query=event%3Apull_request_target.
Weakness: CWE-532
Which versions are affected by CVE-2021-32724?
1 open source package ship an affected version, including check-spelling/check-spelling. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
check-spelling/check-spelling GitHub Actions | All versions | 0.0.19 |
Products include Check-Spelling Check-Spelling.
How do I fix CVE-2021-32724?
Upgrade check-spelling/check-spelling to 0.0.19 or later.
Is CVE-2021-32724 being exploited?
There is no known exploitation of CVE-2021-32724 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as GHSA-g86g-chm8-7r2p.