Affected: CleanStart: mongosh, CleanStart: opensearch-dashboards-fips

CVE-2026-33938 affects multiple packages. This issue is resolved in later releases. See references for individual vulnerability details.

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: npm: handlebars

## Summary

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.

## Description

Handlebars stores `@partial-block` in the `data` frame that is accessible to templates. In nested contexts, a parent frame's `@partial-block` is reachable as `@_parent.partial-block`. Because the data frame is a mutable object, any registered helper that accepts an object reference and assigns properties to it can overwrite `@partial-block` with an attacker-controlled value.

When `{{> @partial-block}}` is subsequently evaluated, `invokePartial` receives the crafted object. The runtime, finding an object that is not a compiled function, falls back to **dynamically compiling** the value via `env.compile()`. If that value is a well-formed Handlebars AST containing injected code, the injected JavaScript runs in the server process.

The `handlebars-helpers` npm package (commonly used with Handlebars) includes several helpers such as `merge` that can be used as the mutation primitive.

## Proof of Concept

Tested with Handlebars 4.7.8 and `handlebars-helpers`:

```javascript const Handlebars = require('handlebars'); const merge = require('handlebars-helpers').object().merge; H…

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Affected: Ubuntu:18.04:LTS: node-handlebars, Ubuntu:20.04:LTS: node-handlebars, Ubuntu:22.04:LTS: node-handlebars, Ubuntu:24.04:LTS: node-handlebars, Ubuntu:25.10: node-handlebars, Ubuntu:26.04:LTS: node-handlebars

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.

Ein Angreifer kann mehrere Schwachstellen in IBM App Connect Enterprise Certified Container ausnutzen, um beliebigen Programmcode auszuführen, vertrauliche Informationen offenzulegen, einen Denial-of-Service-Zustand zu verursachen oder Cross-Site-Scripting-Angriffe durchzuführen.