hbs is an Express view engine wrapper for Handlebars. Version 4.3.0 can crash the Node.js process during output escaping when an async helper, registered with registerAsyncHelper, resolves to an object whose toHTML property is truthy but not callable. Handlebars escapeExpression calls the toHTML method on any value that has a truthy toHTML, so such a value throws a TypeError, and because the async substitution runs on a later tick outside the render function's try/catch, the throw is an uncaught exception that terminates the process without sending a response. Only version 4.3.0 is affected, since the throwing escape was introduced by the fix for CVE-2026-16231 and earlier versions do not escape async helper values. It can be triggered remotely when an async helper resolves to an externally influenced object such as parsed JSON. The issue is fixed in hbs 4.3.1, and users should upgrade to hbs 4.3.1 or later.

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History

Fri, 11 Sep 2026 11:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 11 Sep 2026 10:00:00 +0000

Type Values Removed Values Added
Description hbs is an Express view engine wrapper for Handlebars. Version 4.3.0 can crash the Node.js process during output escaping when an async helper, registered with registerAsyncHelper, resolves to an object whose toHTML property is truthy but not callable. Handlebars escapeExpression calls the toHTML method on any value that has a truthy toHTML, so such a value throws a TypeError, and because the async substitution runs on a later tick outside the render function's try/catch, the throw is an uncaught exception that terminates the process without sending a response. Only version 4.3.0 is affected, since the throwing escape was introduced by the fix for CVE-2026-16231 and earlier versions do not escape async helper values. It can be triggered remotely when an async helper resolves to an externally influenced object such as parsed JSON. The issue is fixed in hbs 4.3.1, and users should upgrade to hbs 4.3.1 or later.
Title hbs vulnerable to Denial of Service via unhandled exception in async helper output escaping
Weaknesses CWE-248
References
Metrics cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-09-11T10:29:11.500Z

Reserved: 2026-09-08T21:42:04.314Z

Link: CVE-2026-87123

cve-icon Vulnrichment

Updated: 2026-09-11T10:28:42.558Z

cve-icon NVD

Status : Received

Published: 2026-09-11T10:16:53.137

Modified: 2026-09-11T11:16:57.387

Link: CVE-2026-87123

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-11T11:30:12Z

Weaknesses