CVE-2026-16231 json
hbs vulnerable to XSS via registerAsyncHelper output-escaping bypass
published 2026-08-25 2 mo ago modified 2026-10-06 33 d ago also EUVD-2026-65392
- cvss
- 8.1
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.4%
- EPSS 0.4% chance of exploitation in 30 days, percentile 34%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- hbs hbs 4.3.0
CISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- total
- Assessed
- 2 mo ago
Exploit prediction
0.40% chance of exploitation in the next 30 days, higher than 34% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 8.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N |
Affected products
- hbs hbs
Classification
- Weakness
-
- CWE-79 Improper Neutralization of Input During Web Page Generation
References
-
github.com
/pillarjs/hbs/security/advisories/GHSA-rg36-rxv9-2m9q
vendor-advisory
-
cna.openjsf.org
/security-advisories.html
vendor-advisory
Sources
- CVE List CVE-2026-16231
- NVD CVE-2026-16231
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.