CVE-2026-16231hbs vulnerable to XSS via registerAsyncHelper output-escaping bypass
Updated under an hour ago ()
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It affects hbs and 1 other product. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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hbs is an Express view engine that wraps Handlebars. Its registerAsyncHelper API bypasses Handlebars' automatic HTML escaping: an async helper returns an opaque placeholder during the first render pass, so the double-brace expression escapes only the placeholder, and after rendering hbs substitutes the placeholder with the raw callback return value without escaping it, across the cached, uncached, and layout render paths. An application that passes attacker-influenced data, for example user-supplied content from a database, into an async helper callback can therefore have arbitrary HTML and JavaScript injected into the server-rendered page, resulting in stored or reflected cross-site scripting. Versions 2.1.0 through 4.2.1 are affected, and the issue is fixed in 4.3.0, which HTML-escapes async helper output. Applications that intentionally emit raw HTML from an async helper can opt in explicitly with hbs.SafeString. Users should upgrade to 4.3.0.
- CVSS
- 8.1 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
- Weakness (CWE)
- CWE-79
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- openjs
- NVD analysis
- Analyzed
- Record last updated
- Aug 25, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
hbs hbs hbs:hbs (from the name) | from 2.1.0 before 4.3.0; 4.3.0 not affected | CNA record |
hbs_project hbs hbs_project:hbs | from 2.1.0 before 4.3.0 | NVD |
References
- https://github.com/pillarjs/hbs/security/advisories/GHSA-rg36-rxv9-2m9qvendor-advisory
- https://cna.openjsf.org/security-advisories.htmlvendor-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.