hbs vulnerable to XSS via registerAsyncHelper output-escaping bypass

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-16231
StatePUBLISHED
Assigneropenjs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-25 10:18:04 UTC
Updated2026-08-31 18:56:59 UTC
Descriptionhbs 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.

Risk And Classification

Primary CVSS: v3.1 8.1 HIGH from ce714d77-add3-4f53-aff5-83d477b104bb

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

EPSS: 0.002270000 probability, percentile 0.132830000 (date 2026-09-01)

Problem Types: CWE-79 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

VersionSourceTypeScoreSeverityVector
3.1ce714d77-add3-4f53-aff5-83d477b104bbSecondary8.1HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
3.1CNACVSS8.1HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Hbs Project Hbs All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Hbs Hbs affected 2.1.0 4.3.0 semver Not specified
CNA Hbs Hbs unaffected 4.3.0 semver Not specified

References

ReferenceSourceLinkTags
github.com/pillarjs/hbs/security/advisories/GHSA-rg36-rxv9-2m9q ce714d77-add3-4f53-aff5-83d477b104bb github.com Vendor Advisory
cna.openjsf.org/security-advisories.html ce714d77-add3-4f53-aff5-83d477b104bb cna.openjsf.org Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: EQSTLab (en)

CNA: UlisesGascon (en)

CNA: bjohansebas (en)

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