VulnerabilityAwaiting Analysis

CVE-2026-106445

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…

CRITICAL 9.2EPSS 0.59%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (0.59%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

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.

CVSS 4.0: 9.2 CRITICALCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
EPSS: 0.59% probability · 48th percentile
Public exploits: None in Exploit-DB
CISA KEV: Not listed
Weakness: CWE-184, CWE-1289
Source: security-advisories@github.com

EPSS trend

EPSS moved from 0.4% on 7 October 2026 to 0.6% on 27 October 2026.

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.