EUVD-2026-76029Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Network reachable but AC:H due to narrow preconditions (registerAsyncHelper plus externally-shaped object with truthy non-callable toHTML); pure availability impact only.
Primary rating from Vendor (ce714d77-add3-4f53-aff5-83d477b104bb).
CVSS VectorVendor: ce714d77-add3-4f53-aff5-83d477b104bb
Lifecycle Timeline
2DescriptionCVE.org
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.
AnalysisAI
Uncaught TypeError in hbs 4.3.0 crashes the Node.js process when an async Handlebars helper resolves to an object with a truthy but non-callable toHTML property. Handlebars' escapeExpression unconditionally invokes toHTML() on any value that exposes it; because async helper substitution executes on a later event-loop tick, the resulting TypeError falls outside the render function's try/catch and becomes a fatal uncaught exception, terminating the entire process without sending a response. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires three concurrent conditions: (1) the application must be running exactly hbs 4.3.0 - no other version is affected; (2) at least one Handlebars helper must be registered using `registerAsyncHelper` rather than a synchronous helper; and (3) that async helper must resolve to a value that is externally influenced (e.g., parsed from request body or query parameters) and carries a truthy but non-callable `toHTML` property. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H yields a base score of 5.9, which reflects an exclusively availability impact with high attack complexity. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade to hbs 4.3.1 or later, which is the vendor-released patch. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-248 – Uncaught Exception
View allSame technique Denial Of Service
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External POC / Exploit Code
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