RCE in Handlebarsjs Handlebars

CVE-2026-33937

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.

Vulnerability class: RCE (Remote Code Execution)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.017 (76.8th percentile), scored .

Low probability of exploitation in the next 30 days, but still tracked. 77th percentile — 76.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-33937: held from 0.017 to 0.017.

EPSS over last 30 days · oldest: 0.017 · newest: 0.017 · change: +0.000

Affected products

Weakness classification (CWE)

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2026-33937?
CVE-2026-33937 is a critical-severity vulnerability in Handlebarsjs Handlebars, classified under Code Injection. CVSS score: 9.8/10. Published 2026-03-27.
How severe is CVE-2026-33937?
Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2026-33937 known to be exploited?
4 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.