CVE-2021-21423
HIGHRebuild-bot workflow may allow unauthorised repository modifications
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
projennpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | projen | ≥ 0.6.0&&< 0.16.41 | 0.16.41 |
| 🐍PyPI | projen | all versions | 0.16.41 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for projen. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update projen to 0.16.41 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21423 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-21423 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-21423. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-21423 in your dependencies?
O3 detects CVE-2021-21423 across npm, PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.