# Prototype Pollution in handlebars

Advisory record · `GHSA-w457-6q6x-cgp9`

- **Identifiers:** `GHSA-w457-6q6x-cgp9` · `CVE-2019-19919`
- **State:** Confirmed
- **Severity:** CVSS 9.8 Critical
- **Critical:** Yes: CVSS 9+
- **Weakness (CWE):** [CWE-74](https://cwe.mitre.org/data/definitions/74.html) · [CWE-1321](https://cwe.mitre.org/data/definitions/1321.html)
- **Tags:** [Other injection](https://agentprime.io/advisories/tag/injection.md) · [Prototype pollution](https://agentprime.io/advisories/tag/prototype-pollution.md)
- **Published:** 26 Dec 2019
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 26 Dec 2019, 17:58 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Critical

Critical, because:

- CVSS score 9.8: 9.0 or more.

How we decide what’s critical: <https://agentprime.io/advisories/critical.md>

## Affected packages

- `handlebars` (npm): affected `>=4.0.0, <4.3.0 || <3.0.8`; fixed in `4.3.0`, `3.0.8`
- `bootstrap-wysihtml5-rails` (RubyGems): affected `>=0.3.3.5, <=0.3.3.8`; no fixed version yet

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 9.8 Critical, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`, from GitHub Advisory Database

- **CISA KEV:** Not listed.
- **EPSS:** 0.071, the 94th percentile, on 9 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

This record came from the full history of the GitHub Advisory Database, published 26 Dec 2019. New records show when each source confirmed them.

## Sources

- [GitHub Advisory Database: GHSA-w457-6q6x-cgp9](https://github.com/advisories/GHSA-w457-6q6x-cgp9)
- [OSV: GHSA-w457-6q6x-cgp9](https://osv.dev/vulnerability/GHSA-w457-6q6x-cgp9)
- <https://nvd.nist.gov/vuln/detail/CVE-2019-19919>
- <https://github.com/wycats/handlebars.js/issues/1558>
- <https://github.com/handlebars-lang/handlebars.js/commit/156061eb7707575293613d7fdf90e2bdaac029ee>
- <https://github.com/handlebars-lang/handlebars.js/commit/90ad8d97ad2933852fb83fcc054699dc99e094db>
- <https://github.com/wycats/handlebars.js/commit/2078c727c627f25d4a149962f05c1e069beb18bc>
- <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-19919>
- <https://github.com/Nerian/bootstrap-wysihtml5-rails/blob/master/vendor/assets/javascripts/bootstrap-wysihtml5/handlebars.runtime.min.js>
- <https://github.com/Nerian/bootstrap-wysihtml5-rails/tree/master/vendor/assets/javascripts/bootstrap-wysihtml5>
- <https://github.com/rubysec/ruby-advisory-db/blob/master/gems/bootstrap-wysihtml5-rails/CVE-2019-19919.yml>
- <https://github.com/wycats/handlebars.js>
- <https://www.tenable.com/security/tns-2021-14>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-w457-6q6x-cgp9>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-w457-6q6x-cgp9/>. Everything for agents: <https://agentprime.io/llms.txt>.