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CVE-2026-33937: Handlebars.js has JavaScript Injection via AST Type Confusion

March 27, 2026

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.

References

  • github.com/advisories/GHSA-2w6w-674q-4c4q
  • github.com/handlebars-lang/handlebars.js
  • github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2
  • github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9
  • github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2w6w-674q-4c4q
  • nvd.nist.gov/vuln/detail/CVE-2026-33937

Code Behaviors & Features

Detect and mitigate CVE-2026-33937 with GitLab Dependency Scanning

Secure your software supply chain by verifying that all open source dependencies used in your projects contain no disclosed vulnerabilities. Learn more about Dependency Scanning →

Affected versions

All versions starting from 4.0.0 before 4.7.9

Fixed versions

  • 4.7.9

Solution

Upgrade to version 4.7.9 or above.

Impact 9.8 CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Learn more about CVSS

Weakness

  • CWE-843: Access of Resource Using Incompatible Type ('Type Confusion')
  • CWE-94: Improper Control of Generation of Code ('Code Injection')

Source file

npm/handlebars/CVE-2026-33937.yml

Spotted a mistake? Edit the file on GitLab.

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