Access of Resource Using Incompatible Type ('Type Confusion') 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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Test your applications- Snyk IDSNYK-JS-HANDLEBARS-15803082
- published29 Mar 2026
- disclosed27 Mar 2026
- creditUnknown
Introduced: 27 Mar 2026
NewCVE-2026-33938 (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 Access of Resource Using Incompatible Type ('Type Confusion') via manipulation of the @partial-block variable in the template data context. An attacker can execute arbitrary JavaScript code on the server by overwriting @partial-block with a crafted Handlebars AST and triggering its evaluation through a subsequent invocation.
Note: This is only exploitable if helpers that accept arbitrary objects are registered and allow mutation of the data context.
Workaround
This vulnerability can be mitigated by using the runtime-only build require('handlebars/runtime'), auditing registered helpers to prevent writing arbitrary values to context objects, and avoiding registration of helpers from third-party packages in contexts where templates or context data can be influenced by untrusted input.