CVE-2026-87123 hbs vulnerable to Denial of Service via unhandled exception in async helper output escaping
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-87123?
CVE-2026-87123 is a medium-severity vulnerability in hbs, published on 11 Sep 2026.
Official 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.
Weakness: CWE-248
Which versions are affected by CVE-2026-87123?
How do I fix CVE-2026-87123?
No fix has been published for CVE-2026-87123 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-87123 being exploited?
There is no known exploitation of CVE-2026-87123 in the wild and no public exploit code.
Sources
Also known as GHSA-3c55-w9jx-p5jr.