Vulnerability · Published Mar 27, 2026 · Assigned by GitHub_M
CVE-2026-33937Handlebars.js has JavaScript Injection via AST Type Confusion
Critical 9.8
In plain English
A critical-severity type confusion in handlebars.js from handlebars-lang. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 1.9% (higher than 80% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | node-handlebars | no fix listed | DEBIAN-CVE-2026-33937 |
| Debian:13 | node-handlebars | no fix listed | DEBIAN-CVE-2026-33937 |
| Debian:14 | node-handlebars | 3:4.7.9-1 | DEBIAN-CVE-2026-33937 |
| Ubuntu:22.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-33937 |
| Ubuntu:24.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-33937 |
| Ubuntu:25.10 | node-handlebars | no fix listed | UBUNTU-CVE-2026-33937 |
| Ubuntu:26.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-33937 |
| Ubuntu:26.10 | node-handlebars | no fix listed | UBUNTU-CVE-2026-33937 |
| npm | handlebars | 4.7.9 | GHSA-2w6w-674q-4c4q |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| handlebars-lang | handlebars.js | >= 4.0.0, < 4.7.9 |
Weakness: CWE-843, CWE-94 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2w6w-674q-4c4q x_refsource_CONFIRM
- https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2 x_refsource_MISC
- https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9 x_refsource_MISC
- https://access.redhat.com/security/cve/CVE-2026-33937 vdb-entry, x_refsource_REDHAT
- RHBZ#2452523 issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33937.json x_sadp-csaf-vex
- https://access.redhat.com/errata/RHSA-2026:34342 vendor-advisory, x_refsource_REDHAT
- https://access.redhat.com/errata/RHSA-2026:10175 vendor-advisory, x_refsource_REDHAT