CVE-2021-21423 Exposure of Version-Control Repository to an Unauthorized Control Sphere in projen

What is CVE-2021-21423?

CVE-2021-21423 is a medium-severity missing authorization vulnerability in projen, published on 6 Apr 2021. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

`projen` is a project generation tool that synthesizes project configuration files such as `package.json`, `tsconfig.json`, `.gitignore`, GitHub Workflows, `eslint`, `jest`, and more, from a well-typed definition written in JavaScript. Users of projen's `NodeProject` project type (including any project type derived from it) include a `.github/workflows/rebuild-bot.yml` workflow that may allow any GitHub user to trigger execution of un-trusted code in the context of the "main" repository (as opposed to that of a fork). In some situations, such untrusted code may potentially be able to commit to the "main" repository. The rebuild-bot workflow is triggered by comments including `@projen rebuild` on pull-request to trigger a re-build of the projen project, and updating the pull request with the updated files. This workflow is triggered by an `issue_comment` event, and thus always executes with a `GITHUB_TOKEN` belonging to the repository into which the pull-request is made (this is in contrast with workflows triggered by `pull_request` events, which always execute with a `GITHUB_TOKEN` belonging to the repository from which the pull-request is made). Repositories that do not have branch protection configured on their default branch (typically `main` or `master`) could possibly allow an untrusted user to gain access to secrets configured on the repository (such as NPM tokens, etc). Branch protection prohibits this escalation, as the managed `GITHUB_TOKEN` would not be able to modify the contents of a protected branch and affected workflows must be defined on the default branch.

Weakness: CWE-527

Which versions are affected by CVE-2021-21423?

5 open source packages ship an affected version, including projen. It affects 1 product.

Products include Projen Project Projen.

How do I fix CVE-2021-21423?

Upgrade projen to 0.16.41 or later.

Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.

Is CVE-2021-21423 being exploited?

There is no known exploitation of CVE-2021-21423 in the wild and no public exploit code.

Public exploit code: 1 proofs of concept on GitHub.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-gg2g-m5wc-vccq, PYSEC-2021-111.