CVE-2026-33940: Handlebarsjs Handlebars code injection (CVSS 8.1)

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.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityHigh

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Handlebarsjs Handlebars≥ 4.0.0 < 4.7.9

Remediation

Fixed in

Handlebarsjs Handlebars≥ 4.7.9

Patch & vendor advisories

References

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-33940 being actively exploited?

CVE-2026-33940 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.79%.

How severe is CVE-2026-33940?

CVE-2026-33940 has a CVSS 3.1 base score of 8.1, rated high. EPSS estimates a 0.79% probability of exploitation.

Which products are affected by CVE-2026-33940?

Affected products include Handlebarsjs Handlebars.

How do I fix CVE-2026-33940?

Upgrade affected software to a fixed version, for example Handlebarsjs Handlebars 4.7.9 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-33940 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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