Security Flaw in Handlebars JavaScript Templates by Handlebars Labs
CVE-2026-33940
What is CVE-2026-33940?
Inversions between 4.0.0 and 4.7.8, a crafted object within the Handlebars template context can effectively bypass conditional guards in the resolvePartial() function. This leads to invokePartial() returning undefined, causing the Handlebars runtime to erroneously treat the unresolved partial as requiring compilation. As a result, this can trigger the execution of arbitrary JavaScript commands on the server, particularly if the attacker controls the data returned during a dynamic partial lookup. The issue is validated to be remedied in version 4.7.9, alongside several recommended workarounds. Users are urged to either use the runtime-only build of Handlebars or ensure that contextual data is rigorously sanitized before rendering.
Affected Version(s)
handlebars.js >= 4.0.0, < 4.7.9