CVE-2019-19919: Prototype Pollution in handlebars

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 7.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2019-12-20 · updated 2026-06-17
Weakness: CWE-1321

Description

Versions of handlebars prior to 4.3.0 are vulnerable to Prototype Pollution leading to Remote Code Execution. Templates may alter an Object's __proto__ and __defineGetter__ properties, which may allow an attacker to execute arbitrary code through crafted payloads.

Affected products

Handlebars.Js Project Handlebars.Js: 1.0.6, 1.0.7, 1.0.8, 1.0.9, 1.0.10, 1.0.11 (+37)
Tenable.sc: before 5.19.0 — fixed in 5.19.0
Npm Handlebars: from 4.0.0 before 4.3.0; before 3.0.8 — fixed in 4.3.0, 3.0.8
Rubygems Bootstrap-Wysihtml5-Rails: from 0.3.3.5 through 0.3.3.8; 0.3.3.5, 0.3.3.6, 0.3.3.7, 0.3.3.8

How to fix

Upgrade to a fixed version: Tenable.sc 5.19.0; Npm Handlebars 4.3.0, 3.0.8. Check the vendor advisory for mitigations.

References

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