CVE-2019-20922: Regular Expression Denial of Service in Handlebars

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 3.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2020-09-30 · updated 2026-06-17
Weakness: CWE-400

Description

Handlebars before 4.4.5 allows Regular Expression Denial of Service (ReDoS) because of eager matching. The parser may be forced into an endless loop while processing crafted templates. This may allow attackers to exhaust system resources.

Affected products

handlebars-lang handlebars.js: from 4.0.0 before 4.4.5 — fixed in 4.4.5
Npm Handlebars: from 4.0.0 before 4.4.5 — fixed in 4.4.5

How to fix

Upgrade to a fixed version: handlebars-lang handlebars.js 4.4.5; Npm Handlebars 4.4.5. Check the vendor advisory for mitigations.

References

https://github.com/handlebars-lang/handlebars.js/commit/8d5530ee2c3ea9f0aee3fde310b9f36887d00b8b
https://snyk.io/vuln/SNYK-JS-HANDLEBARS-480388
https://www.npmjs.com/advisories/1300
https://github.com/handlebars-lang/handlebars.js/commit/8d5530ee2c3ea9f0aee3fde310b9f36887d00b8b
https://snyk.io/vuln/SNYK-JS-HANDLEBARS-480388
https://www.npmjs.com/advisories/1300

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