# CVE-2026-33938: Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block

CVE-2026-33938 is fixed in node-handlebars on 1 platform by DEBIAN-CVE-2026-33938 (version 3:4.7.9-1), released March 27, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-33938
- Priority: High
- CVSS: 8.1 (Important)
- EPSS: 0.0072
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Mar 27, 2026
- Weakness: Improper Control of Generation of Code ('Code Injection')
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33938

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | node-handlebars Debian 14 | 3:4.7.9-1 | [DEBIAN-CVE-2026-33938](https://patchblox.com/security/data/fix/linux/debian-cve-2026-33938.md) | Mar 27, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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