Improper Encoding or Escaping of Output Affecting handlebars package, versions >=4.0.0 <4.7.9
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Start learning- Snyk IDSNYK-JS-HANDLEBARS-15807040
- published29 Mar 2026
- disclosed27 Mar 2026
- creditGyde04
Introduced: 27 Mar 2026
NewCVE-2026-33941 (opens in a new tab)How to fix?
Upgrade handlebars to version 4.7.9 or higher.
Overview
handlebars is an extension to the Mustache templating language.
Affected versions of this package are vulnerable to Improper Encoding or Escaping of Output through the CLI precompiler in lib/precompiler.js. An attacker can execute arbitrary JavaScript in the generated bundle by supplying crafted template filenames or CLI options such as --namespace, --commonjs, --handlebarPath, or --map. The issue affects the precompiler output path used by bin/handlebars / lib/precompiler.js, where untrusted names and option values were concatenated into emitted JavaScript without escaping.
**Workarounds**
- Validate template filenames and CLI option values before invoking the precompiler and reject values containing JavaScript string-escaping or statement-breaking characters.
- Use a fixed, trusted namespace string rather than passing it from the command line in automated pipelines.
- Run the precompiler in a sandboxed environment with limited write access.