CVE-2026-87123: hbs Uncaught Exception

Vulnerability summary

CVE-2026-87123 is a medium (CVSS 5.9) Uncaught Exception vulnerability in hbs. EPSS estimates a 0.41% chance of exploitation in the next 30 days, higher than 34.3% of scored vulnerabilities.

Timeline

1. 11-09-2026
   PublishedVulnerability first disclosed.
2. 11-09-2026
   Last modifiedVulnerability information updated.

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.

• CWE-248Uncaught ExceptionAn exception is thrown from a function, but it is not caught.