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.

• 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://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-3mfm-83xf-c92r x_refsource_CONFIRM
• https://access.redhat.com/security/cve/CVE-2026-33938 vdb-entryx_refsource_REDHAT
• https://bugzilla.redhat.com/show_bug.cgi?id=2452525 issue-trackingx_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-advisoryx_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:10175 vendor-advisoryx_refsource_REDHAT