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.
Affected products
handlebarsjs: handlebars
References8
- github.com/handlebars-lang/handlebars.js/security/advisories/GH… ExploitVendor Advisory
- github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26… Patch
- github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9 Release Notes
- access.redhat.com/errata/RHSA-2026:10175
- access.redhat.com/errata/RHSA-2026:34342
- access.redhat.com/security/cve/CVE-2026-33937
- bugzilla.redhat.com/show_bug.cgi?id=2452523
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33937…
Metrics
- CVSS 3.1
-
9.8
CRITICAL
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - EPSS — exploit probability
- 2% percentile: 80 · as of 12 November 2026
- CWE
- CWE-94CWE-843
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.