Handlebars.js has a Property Access Validation Bypass in container.lookup
Summary
In lib/handlebars/runtime.js, the container.lookup() function uses container.lookupProperty() as a gate check to enforce prototype-access controls, but then discards the validated result and performs a second, unguarded property access (depths[i][name]). This Time-of-Check Time-of-Use (TOCTOU) pattern means the security check and the actual read are decoupled, and the raw access bypasses any sanitization that lookupProperty may perform.
Only relevant when the compat compile option is enabled ({compat: true}), which activates depthedLookup in lib/handlebars/compiler/javascript-compiler.js.
Description
The vulnerable code in lib/handlebars/runtime.js (lines 137–144):
lookup: function (depths, name) {
const len = depths.length;
for (let i = 0; i < len; i++) {
let result = depths[i] && container.lookupProperty(depths[i], name);
if (result != null) {
return depths[i][name]; // BUG: should be `return result;`
}
}
},container.lookupProperty() (lines 119–136) enforces hasOwnProperty checks and resultIsAllowed() prototype-access controls. However, container.lookup() only uses lookupProperty as a boolean gate — if the gate passes (result != null), it then performs an independent, raw depths[i][name] access that circumvents any transformation or wrapped value that lookupProperty may have returned.
Workarounds
- Avoid enabling
{ compat: true }when rendering templates that include untrusted data. - Ensure context data objects are plain JSON (no Proxies, no getter-based accessor properties).
Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Paquete de npm | handlebars | >= 4.0.0, < 4.7.9 | 4.7.9 |
Referencias
- https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-442j-39wm-28r2
- https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2
- https://github.com/handlebars-lang/handlebars.js
- https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9
- Vector CVSS
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N- Debilidad (CWE)
CWE-367- Plataforma
- npm
- Paquete
handlebars- Publicada
- 29.03.2026
- Actualizado
- 11.10.2026 10:22
Fuentes y licencias
OSV / GitHub Advisory Database - GHSA-442j-39wm-28r2 - CC BY 4.0
Historial de vulnerabilidades: handlebars
Todas las vulnerabilidades publicadas de este paquete (Paquete de npm), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.
- Entradas en total
- 22
- Primera → última
- 10.2018 10.2026
- Sin corrección
- 0
- Explotada en ataques
- 0
Distribución por gravedad
- Crítica 6
- Alta 10
- Media 5
- Baja 1
Divulgaciones por año
- 2018: 1
- 2019: 2
- 2020: 4
- 2021: 1
- 2022: 3
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 11
-
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