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

> Attackers can trigger untrusted code execution and access secrets in projen projects lacking branch protection via rebuild-bot workflow comments.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Apr 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-gg2g-m5wc-vccq, PYSEC-2021-111

## 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 (Exposure of Version-Control Repository to an Unauthorized Control Sphere)

## Which versions are affected by CVE-2021-21423?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `projen` | PyPI | All versions | 0.16.41 |
| `projen` | PyPI | All versions | 0.16.41 |
| `projen` | PyPI | All versions | 0.16.41 |
| `projen` | npm | From 0.6.0 | 0.16.41 |
| `projen` | npm | From 0.6.0 | 0.16.41 |

Products: Projen Project Projen.

## How do I fix CVE-2021-21423?

Upgrade projen to 0.16.41 or later.

## 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:

- Authorized security-research lab reproducing CVE-2021-21423 (GHSA-gg2g-m5wc-vccq): projen rebuild-bot pwn request via issue_comment (github_poc): https://github.com/pvharmo2/gha-lab-b9842b12c0

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21423 and fix it if it is affected.

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

Affected packages and fixed versions:
- projen (PyPI): affected all versions; fixed in 0.16.41
- projen (PyPI): affected all versions; fixed in 0.16.41
- projen (PyPI): affected all versions; fixed in 0.16.41
- projen (npm): affected from 0.6.0; fixed in 0.16.41
- projen (npm): affected from 0.6.0; fixed in 0.16.41

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-21423/ (Markdown: https://insights.sbomify.com/CVE-2021-21423/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21423
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21423
- OSV: https://osv.dev/vulnerability/CVE-2021-21423

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21423/
Summaries are generated and may contain mistakes; the official description above is the record.