Vulnerability · Published Mar 27, 2026 · Assigned by GitHub_M
CVE-2026-33938Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block
High 8.1
In plain English
A high-severity code injection 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 0.7% (higher than 54% of all known vulnerabilities). 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, the `@partial-block` special variable is stored in the template data context and is reachable and mutable from within a template via helpers that accept arbitrary objects. When a helper overwrites `@partial-block` with a crafted Handlebars AST, a subsequent invocation of `{{> @partial-block}}` compiles and executes that AST, enabling arbitrary JavaScript execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). The `compile()` method is absent, eliminating the vulnerable fallback path. Second, audit registered helpers for any that write arbitrary values to context objects. Helpers should treat context data as read-only. Third, avoid registering helpers from third-party packages (such as `handlebars-helpers`) in contexts where templates or context data can be influenced by untrusted input.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | node-handlebars | no fix listed | DEBIAN-CVE-2026-33938 |
| Debian:13 | node-handlebars | no fix listed | DEBIAN-CVE-2026-33938 |
| Debian:14 | node-handlebars | 3:4.7.9-1 | DEBIAN-CVE-2026-33938 |
| Ubuntu:22.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-33938 |
| Ubuntu:24.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-33938 |
| Ubuntu:25.10 | node-handlebars | no fix listed | UBUNTU-CVE-2026-33938 |
| Ubuntu:26.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-33938 |
| Ubuntu:26.10 | node-handlebars | no fix listed | UBUNTU-CVE-2026-33938 |
| npm | handlebars | 4.7.9 | GHSA-3mfm-83xf-c92r |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| handlebars-lang | handlebars.js | >= 4.0.0, < 4.7.9 |
Weakness: CWE-94, CWE-843, CWE-917 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-3mfm-83xf-c92r 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-2026-33938 vdb-entry, x_refsource_REDHAT
- RHBZ#2452525 issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33938.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