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VulnerabilityPublished Updated

CVE-2026-33916: handlebars.js · Cross-site Scripting

Affects handlebars.jsSource CVE Database V5

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Not known to be exploited · CVSS 4.7 Medium : upgrade to 4.7.9 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
4.7Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 20% 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:R/S:C/C:L/I:L/A:N

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 and handlebars 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
  • <4.7.9 >=4.0.0
Fixed in
  • 4.7.9

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

AI-suggested

A fixed version, 4.7.9, is available and should be applied to remediate this vulnerability. As workarounds, applications can apply Object.freeze(Object.prototype) early during startup to prevent prototype pollution, though this may break other libraries. Alternatively, using the Handlebars runtime-only build (handlebars/runtime), which does not compile templates, can reduce the attack surface. Patch status is confirmed fixed in version 4.7.9.

Description

Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `resolvePartial()` in the Handlebars runtime resolves partial names via a plain property lookup on `options.partials` without guarding against prototype-chain traversal. When `Object.prototype` has been polluted with a string value whose key matches a partial reference in a template, the polluted string is used as the partial body and rendered without HTML escaping, resulting in reflected or stored XSS. Version 4.7.9 fixes the issue. Some workarounds are available. Apply `Object.freeze(Object.prototype)` early in application startup to prevent prototype pollution. Note: this may break other libraries, and/or use the Handlebars runtime-only build (`handlebars/runtime`), which does not compile templates and reduces the attack surface.

References

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