{"id":"CVE-2021-21423","aliases":["GHSA-gg2g-m5wc-vccq","PYSEC-2021-111"],"title":"Rebuild-bot workflow may allow unauthorised repository modifications","summary":"Rebuild-bot workflow may allow unauthorised repository modifications","severity":"medium","cvss":6.8,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N","vendor":"projen","product":"projen","ecosystem":"npm","affected":["projen >= 0.6.0, < 0.16.41","projen < 0.16.41"],"patched":["projen 0.16.41","projen 0.16.41"],"published":"2021-04-06","updated":"2026-07-08","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-gg2g-m5wc-vccq","references":[{"url":"https://github.com/projen/projen/security/advisories/GHSA-gg2g-m5wc-vccq"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21423"},{"url":"https://github.com/projen/projen/commit/36030c6a4b1acd0054673322612e7c70e9446643"},{"url":"https://github.com/projen/projen"},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/projen/PYSEC-2021-111.yaml"},{"url":"https://www.npmjs.com/package/projen"}],"tags":["osv","npm","exploit-available"],"epss":0.01381,"epssPercentile":0.70971,"ingestedAt":"2026-07-08T18:25:49.708Z","exploits":{"github":1,"githubRepos":["https://github.com/pvharmo2/gha-lab-b9842b12c0"],"checkedAt":"2026-09-26T09:05:26.235Z"},"exploitAvailable":true,"slug":"CVE-2021-21423","body":"## Overview\n\n### Impact\n\n`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.\n\nThe 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).\n\nRepositories 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. \n\n### Patches\n\nThe issue was mitigated in version `0.16.41` of the `projen` tool, which removes the `issue_comment` trigger from this workflow. Version `0.17.0` of projen completely removes the `rebuild-bot.yml` workflow.\n\n### Workarounds\n\nThe recommended way to address the vulnerability is to upgrade `projen`. Users who cannot upgrade `projen` may also remove the `.github/workflows/rebuild-bot.yml` file and add it to their `.gitignore` file (via `projenrc.js`) to mitigate the issue.\n\n### References\n\nThe `rebuild-bot.yml` workflow managed by `projen` is only one occurrence of a GitHub Workflows mis-configuration, but it may also be present in other workflows not managed by `projen` (either hand-written, or managed by other tools). For more information on this class of issues, the [Keeping your GitHub Actions and workflows secure: Preventing pwn requests][1] article provides a great overview of the problem.\n \n\n[1]: https://securitylab.github.com/research/github-actions-preventing-pwn-requests\n\n## Affected packages\n\n- `projen >= 0.6.0, < 0.16.41`\n- `projen < 0.16.41`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `projen 0.16.41`\n- `projen 0.16.41`","depth":"twilight","depthScore":50,"depthScoreParts":{"impact":37.4,"likelihood":0.3,"exploitation":12,"ransomware":0},"changes":[{"seq":4501,"id":"CVE-2021-21423","ts":1788887186008,"field":"exploit_available","old":"false","new":"true"},{"seq":3384,"id":"CVE-2021-21423","ts":1788886303731,"field":"exploit_available","old":"true","new":"false"},{"seq":2239,"id":"CVE-2021-21423","ts":1788882973362,"field":"exploit_available","old":"false","new":"true"},{"seq":1268,"id":"CVE-2021-21423","ts":1788882385021,"field":"exploit_available","old":"true","new":"false"},{"seq":382,"id":"CVE-2021-21423","ts":1788881820355,"field":"exploit_available","old":"false","new":"true"}]}