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High, CVSS 7.6amended

Rebuild-bot workflow may allow unauthorised repository modifications

CVE-2021-21423GHSA-gg2g-m5wc-vccq

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (projen 0.16.41; projen 0.16.41), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm projen

    Affected
    >= 0.6.0, < 0.16.41
    Fixed in
    0.16.41

  • PyPI projen

    Affected
    < 0.16.41
    Fixed in
    0.16.41

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
7.6 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2021-21423: 1.39% estimated exploitation activity in the next 30 days; percentile 72.39 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact 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 issuecomment event, and thus always executes with a GITHUBTOKEN belonging to the repository into which the pull-request is made (this is in contrast with…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-gg2g-m5wc-vccq

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-gg2g-m5wc-vccq

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2021-21423

Advisory: Rebuild-bot workflow may allow unauthorised repository modifications
IDs: CVE-2021-21423, GHSA-gg2g-m5wc-vccq
Record: https://patchnext.com/advisories/cve-2021-21423 (revision 3, source checked 26 Oct 2026, 12:31 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: projen 0.16.41; projen 0.16.41. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm projen: affected >= 0.6.0, < 0.16.41; fixed in 0.16.41
- PyPI projen: affected < 0.16.41; fixed in 0.16.41

## Suggested inspection (read-only)
- `npm ls projen --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- `python -m pip show projen`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on projen.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-gg2g-m5wc-vccq (OSV record GHSA-gg2g-m5wc-vccq lists affected ranges: npm projen >=0.6.0 =0 <0.16.41 (fixed))
- Verified: https://github.com/advisories/GHSA-gg2g-m5wc-vccq (GitHub-reviewed advisory GHSA-gg2g-m5wc-vccq lists affected ranges: npm projen >=0.6.0 =0 <0.16.41)

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