Vulnerability Description
Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `Handlebars.compile()` accepts a pre-parsed AST object in addition to a template string. The `value` field of a `NumberLiteral` AST node is emitted directly into the generated JavaScript without quoting or sanitization. An attacker who can supply a crafted AST to `compile()` can therefore inject and execute arbitrary JavaScript, leading to Remote Code Execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. Validate input type before calling `Handlebars.compile()`; ensure the argument is always a `string`, never a plain object or JSON-deserialized value. Use the Handlebars runtime-only build (`handlebars/runtime`) on the server if templates are pre-compiled at build time; `compile()` will be unavailable.
CVSS Score
CRITICAL
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Handlebarsjs | Handlebars | >= 4.0.0, < 4.7.9 |
Related Weaknesses (CWE)
References
- https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084cPatch
- https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9Release Notes
- https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2w6w-6ExploitVendor Advisory
FAQ
What is CVE-2026-33937?
CVE-2026-33937 is a vulnerability with a CVSS score of 9.8 (CRITICAL). Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `Handlebars.compile()` accepts a pre-parsed AST object in addition to a template string....
How severe is CVE-2026-33937?
CVE-2026-33937 has been rated CRITICAL with a CVSS base score of 9.8/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-33937?
Check the references section above for vendor advisories and patch information. Affected products include: Handlebarsjs Handlebars.