CVE-2026-33940

Summary

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.

Affected Software

VendorProductVersion RangeStatus
handlebars-langhandlebars.js>= 4.0.0, < 4.7.9affected

Weaknesses

  • CWE-94: CWE-94: Improper Control of Generation of Code ('Code Injection')
  • CWE-843: CWE-843: Access of Resource Using Incompatible Type ('Type Confusion')

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: poc
    • Automatable: no
    • Technical Impact: total

handlebars.js: Handlebars.js: Arbitrary code execution via crafted template context

Additional References

References