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High severity8.1NVD Advisory· Published Mar 27, 2026· Updated Mar 31, 2026

CVE-2026-33940

CVE-2026-33940

Description

Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, a crafted object placed in the template context can bypass all conditional guards in resolvePartial() and cause invokePartial() to return undefined. The Handlebars runtime then treats the unresolved partial as a source that needs to be compiled, passing the crafted object to env.compile(). Because the object is a valid Handlebars AST containing injected code, the generated JavaScript executes arbitrary commands on the server. The attack requires the adversary to control a value that can be returned by a dynamic partial lookup. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (require('handlebars/runtime')). Without compile(), the fallback compilation path in invokePartial is unreachable. Second, sanitize context data before rendering: Ensure no value in the context is a non-primitive object that could be passed to a dynamic partial. Third, avoid dynamic partial lookups ({{> (lookup ...)}}) when context data is user-controlled.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
handlebarsnpm
>= 4.0.0, < 4.7.94.7.9

Affected products

46

Patches

Vulnerability mechanics

References

5

News mentions

0

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