Remote code execution in handlebars when compiling templates

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2021-23369: 7.03% estimated exploitation activity in the next 30 days; percentile 94.19 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

The package handlebars before 4.7.7 are vulnerable to Remote Code Execution (RCE) when selecting certain compiling options to compile templates coming from an untrusted source.

Published by the source

6 May 2021, 15:57 UTC

Last modified by the source

10 Sep 2026, 03:49 UTC

Source last checked

26 Oct 2026, 12:29 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-f2jv-r9rf-7988

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-f2jv-r9rf-7988

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# Patch Next advisory brief: CVE-2021-23369

Advisory: Remote code execution in handlebars when compiling templates
IDs: CVE-2021-23369, GHSA-f2jv-r9rf-7988
Record: https://patchnext.com/advisories/cve-2021-23369 (revision 2, source checked 26 Oct 2026, 12:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.webjars.bowergithub.wycats:handlebars.js 4.7.7; handlebars 4.7.7; org.webjars.npm:handlebars 4.7.7; org.webjars:handlebars 4.7.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.webjars.bowergithub.wycats:handlebars.js: affected < 4.7.7; fixed in 4.7.7
- npm handlebars: affected < 4.7.7; fixed in 4.7.7
- Maven org.webjars.npm:handlebars: affected < 4.7.7; fixed in 4.7.7
- Maven org.webjars:handlebars: affected < 4.7.7; fixed in 4.7.7

## Suggested inspection (read-only)
- Maven org.webjars.bowergithub.wycats:handlebars.js: check the installed version with your package manager.
- `npm ls handlebars --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- Maven org.webjars.npm:handlebars: check the installed version with your package manager.
- Maven org.webjars:handlebars: check the installed version with your package manager.

## 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 org.webjars.bowergithub.wycats:handlebars.js, handlebars, org.webjars.npm:handlebars, org.webjars:handlebars.
- 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-f2jv-r9rf-7988 (OSV record GHSA-f2jv-r9rf-7988 lists affected ranges: npm handlebars >=0 =0 =0 =0 <4.7.7 (fixed))
- Verified: https://github.com/advisories/GHSA-f2jv-r9rf-7988 (GitHub-reviewed advisory GHSA-f2jv-r9rf-7988 lists affected ranges: npm handlebars >=0 =0 =0 =0 <4.7.7)

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