Vulnerability · Published Oct 6, 2026 · Assigned by GitHub_M
CVE-2026-106445Handlebars: JavaScript Injection via Own Property Check Bypass
Critical 9.2
In plain English
A critical-severity security flaw in handlebars.js from handlebars-lang. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 48% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.
Official description
Handlebars provides the power necessary to let users build semantic templates. From 3.0.0 until 4.7.10, Handlebars lookupProperty returns Function.prototype.constructor before applying the prototype-access deny list because constructor is an own property of Function.prototype. When an attacker can render a controlled template with allowProtoMethodsByDefault enabled and an accessible function in the template context, the template can traverse from that function through its prototype to Function.prototype and then obtain the Function constructor through the own-property bypass. This permits attacker-controlled JavaScript to execute with the server application's privileges. This issue is fixed in version 4.7.10.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | node-handlebars | no fix listed | DEBIAN-CVE-2026-106445 |
| Debian:13 | node-handlebars | no fix listed | DEBIAN-CVE-2026-106445 |
| Debian:14 | node-handlebars | 3:4.7.10-1 | DEBIAN-CVE-2026-106445 |
| Ubuntu:22.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-106445 |
| Ubuntu:24.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-106445 |
| Ubuntu:26.04:LTS | node-handlebars | no fix listed | UBUNTU-CVE-2026-106445 |
| Ubuntu:26.10 | node-handlebars | no fix listed | UBUNTU-CVE-2026-106445 |
| npm | handlebars | 4.7.10 | GHSA-p8wg-vrv2-v86f |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| handlebars-lang | handlebars.js | >= 3.0.0, < 4.7.10 |
Weakness: CWE-184, CWE-1289 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
References
- https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-vrv2-v86f x_refsource_CONFIRM
- https://github.com/handlebars-lang/handlebars.js/pull/2185 x_refsource_MISC
- https://github.com/handlebars-lang/handlebars.js/commit/ceec388abe1d1aac8f6369860d5f390fa71ef4fa x_refsource_MISC
- https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.10 x_refsource_MISC