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VulnerabilityPublished Updated

CVE-2026-33940: handlebars.js · Code Injection

Affects handlebars.jsSource CVE Database V5

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Not known to be exploited · CVSS 8.1 High : upgrade to 4.7.9 soon.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
8.1High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.7% chance of exploitation in 30 days – higher than 53% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 4.7.9
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 27 Mar 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade handlebars.js to 4.7.9.

Affected software

ProductAffectedFixed in
handlebars-langhandlebars.jsAffected
  • >=4.0.0 <4.7.9
Fixed in
  • 4.7.9
npmhandlebarspkg:npm/handlebarsOther threatsAffected
  • >=4.0.0 <=4.7.8
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

An official fix is available in Handlebars.js version 4.7.9. Users should upgrade to this version to remediate the vulnerability. If upgrading immediately is not possible, apply workarounds: use the runtime-only build to avoid fallback compilation paths, sanitize all context data to ensure no non-primitive objects can be passed as dynamic partials, and avoid dynamic partial lookups when context data is user-controlled.

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.

References

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