CVE-2026-87123
hbs vulnerable to Denial of Service via unhandled exception in async helper output escaping
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.
INFO
Published Date :
Sept. 11, 2026, 10:16 a.m.
Last Modified :
Sept. 16, 2026, 7:40 p.m.
Remotely Exploit :
No
Source :
ce714d77-add3-4f53-aff5-83d477b104bb
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | ce714d77-add3-4f53-aff5-83d477b104bb |
Solution
- Upgrade hbs to version 4.3.1 or later.
- Ensure async helpers resolve to callable toHTML properties.
- Avoid externally influenced objects in async helper resolutions.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-87123.
| URL | Resource |
|---|---|
| https://cna.openjsf.org/security-advisories.html | |
| https://github.com/pillarjs/hbs/security/advisories/GHSA-3c55-w9jx-p5jr |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-87123 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-87123
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-87123 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-87123 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Sep. 11, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-87123', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-09-11T10:28:38.308689Z'} -
New CVE Received by ce714d77-add3-4f53-aff5-83d477b104bb
Sep. 11, 2026
Action Type Old Value New Value 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. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-248 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/87xxx/CVE-2026-87123.json">CVE-2026-87123</a> Added Reference https://cna.openjsf.org/security-advisories.html Added Reference https://github.com/pillarjs/hbs/security/advisories/GHSA-3c55-w9jx-p5jr