CVE-2026-33937

CRITICAL

Handlebars.js has JavaScript Injection via AST Type Confusion

Title source: cna
STIX 2.1

Exploitation Summary

EIP tracks 2 public exploits for CVE-2026-33937. PoCs published by EQSTLab, dinhvaren.

AI-analyzed exploit summary This repository contains a functional exploit for CVE-2026-33937, leveraging Handlebars AST injection to achieve remote code execution (RCE) via crafted template data. The exploit includes a Dockerized vulnerable environment and an interactive Python script to execute arbitrary commands.

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.

Exploits (2)

nomisec WORKING POC
by EQSTLab · poc
https://github.com/EQSTLab/CVE-2026-33937

This repository contains a functional exploit for CVE-2026-33937, leveraging Handlebars AST injection to achieve remote code execution (RCE) via crafted template data. The exploit includes a Dockerized vulnerable environment and an interactive Python script to execute arbitrary commands.

Classification
Working Poc 95%
Attack Type
Rce
Complexity
Moderate
Reliability
Reliable
Target: Handlebars v4.7.6
No auth needed
Prerequisites: Target running vulnerable Handlebars version · Access to the /api/email/preview endpoint
devstral-2 · analyzed Apr 22, 2026 Full analysis →
nomisec WORKING POC
by dinhvaren · poc
https://github.com/dinhvaren/cve-2026-33937

This repository contains a functional exploit for CVE-2026-33937, demonstrating an RCE vulnerability in Handlebars.js via AST type confusion. The PoC leverages a crafted AST object to inject arbitrary JavaScript code during template compilation.

Classification
Working Poc 95%
Attack Type
Rce
Complexity
Moderate
Reliability
Reliable
Target: Handlebars.js (version not specified)
No auth needed
Prerequisites: Ability to send crafted AST objects to a Handlebars.js template compilation endpoint
devstral-2 · analyzed Apr 08, 2026 Full analysis →

Scores

CVSS v3 9.8
EPSS 0.0024
EPSS Percentile 47.7%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CISA SSVC

Vulnrichment
Exploitation poc
Automatable yes
Technical Impact total

Details

CWE
CWE-843 CWE-94
Status published
Products (3)
handlebars-lang/handlebars.js >= 4.0.0, < 4.7.9
handlebarsjs/handlebars 4.0.0 - 4.7.9
npm/handlebars 4.0.0 - 4.7.9npm
Published Mar 27, 2026
Tracked Since Mar 29, 2026