# Handlebars Denial of Service in template parser

Source: https://junglewise.ai/threats/handlebars-denial-of-service-in-template-parser-7f538b11  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2020-09-03. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

Severity: info · Published 2020-09-03

Handlebars is a popular templating engine used by web applications to generate dynamic content. A vulnerability in versions 4.0.0 through 4.4.4 allows attackers to supply specially crafted templates that force the parser into an infinite loop, consuming system resources and causing the application to become unresponsive or crash.

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, published 3 September 2020.

**Which products and versions are affected?** handlebars (npm) SEMVER:introduced=4.0.0,fixed=4.4.5.

**Is there a fix for This vulnerability?** Yes. handlebars (npm): upgrade to 4.4.5 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 4.4.5 or later

  ```sh
  npm install handlebars@4.4.5
  ```


## Technical details

The vulnerability is a Denial of Service (CWE-400: Uncontrolled Resource Consumption) in the Handlebars template parser. When processing specially-crafted templates, the parser can enter an endless loop that exhausts system resources (CPU, memory). The attack requires the application to accept and parse untrusted template input. The vulnerability affects Handlebars versions 4.0.0 through 4.4.4; a fix is available in version 4.4.5 and later.

## Affected products

- Handlebars Handlebars 4.0.0 through 4.4.4

## Timeline

- 2020-09-03: disclosed
- 2020-09-03: patched: Fixed in version 4.4.5

## References

- [https://www.npmjs.com/advisories/1300](https://www.npmjs.com/advisories/1300)

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