# CVE-2026-87123: hbs vulnerable to Denial of Service via unhandled exception in async helper output escaping


- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 11 Sep 2026
- **Updated:** 11 Sep 2026
- **Also known as:** GHSA-3c55-w9jx-p5jr

## 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 (Uncaught Exception)

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-87123 and fix it if it is affected.

What it is: CVE-2026-87123 is a medium-severity vulnerability in hbs, published on 11 Sep 2026. 
Exploitation: There is no known exploitation of CVE-2026-87123 in the wild and no public exploit code.

Affected product: hbs. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-87123/ (Markdown: https://insights.sbomify.com/CVE-2026-87123/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-87123
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-87123
- OSV: https://osv.dev/vulnerability/CVE-2026-87123

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-87123/
Summaries are generated and may contain mistakes; the official description above is the record.