# Handlebars prototype pollution in template processing

Source: https://junglewise.ai/threats/handlebars-prototype-pollution-in-template-processing-676d30e6  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2020-09-04. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

Severity: info · CVSS 7.5 · Published 2020-09-04

Handlebars is a popular templating engine used to generate dynamic HTML and text content in web applications. Versions prior to 3.0.8 or 4.5.3 contain a prototype pollution vulnerability that allows attackers to inject malicious code through specially crafted templates, potentially crashing applications or executing arbitrary code depending on how the templating engine is used.

Technologies: [handlebars (npm)](https://junglewise.ai/threats/technologies/npm-handlebars). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Informational severity, with a CVSS score of 7.5, published 4 September 2020.

**Which products and versions are affected?** handlebars (npm) SEMVER:introduced=0,fixed=3.0.8.

**Is there a fix for This vulnerability?** Yes. handlebars (npm): upgrade to 3.0.8 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is This vulnerability attacked?** It is attacked over the network, in a software library.

**Am I affected?** Check whether you run handlebars (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- handlebars (npm): upgrade to 3.0.8 or later

  ```sh
  npm install handlebars@3.0.8
  ```


## Technical details

The vulnerability is a prototype pollution flaw (CWE-1321) in Handlebars template processing. An attacker can craft a malicious template that modifies properties on the Object prototype, affecting the behavior of all objects in the application. The attack requires the application to process untrusted template input. Depending on the application context and how the prototype is modified, this can lead to denial of service (application crash) or in specific conditions, arbitrary code execution. Patches are available in versions 3.0.8, 4.5.3, and later.

## Affected products

- Handlebars Handlebars versions prior to 3.0.8 or 4.x versions prior to 4.5.3

## Timeline

- 2020-09-04: disclosed

## References

- [https://www.npmjs.com/advisories/1325](https://www.npmjs.com/advisories/1325)

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