EUVD-2026-93952
GHSA-p8wg-vrv2-v86f
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
AC:H because exploitation requires the non-default allowProtoMethodsByDefault option and a function in context; PR:N since the attacker needs no auth; S:U and C/I/A:H for full RCE in the app's own authority.
Primary rating from Vendor (github).
CVSS VectorVendor: github
Lifecycle Timeline
6Blast Radius
ecosystem impact- 3 npm packages depend on handlebars (1 direct, 2 indirect)
Ecosystem-wide dependent count for version 4.0.0.
DescriptionCVE.org
Handlebars provides the power necessary to let users build semantic templates. From 4.0.0 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.
Articles & Coverage 2
AnalysisAI
Server-side remote code execution affects Handlebars versions 4.0.0 through releases prior to 4.7.10, where a flaw in the lookupProperty prototype-access check lets a rendered template reach Function.prototype.constructor and obtain the JavaScript Function constructor, executing attacker-supplied code with the server application's privileges. Exploitation is conditional: an unauthenticated remote attacker must be able to render a template whose source they control, the runtime must have allowProtoMethodsByDefault enabled (not the default configuration), and the template context must expose an accessible function value that can be traversed via __proto__. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Three specific conditions must all hold: (1) the application must render a template whose content is attacker-controlled; (2) the runtime must be configured with allowProtoMethodsByDefault enabled - this is NOT the default, since Handlebars blocks prototype method access out of the box, so default deployments are not exploitable; and (3) the template context must expose an accessible function value that the attacker can traverse (e.g. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | This is a server-side remote code execution flaw (CWE-184, incomplete disallowed-input list) in Handlebars, an extremely popular JavaScript templating library, carrying a CVSS 4.0 base score of 9.2 (Critical) with vector AV:N/AC:L/AT:P/PR:N/UI:N and full High confidentiality/integrity/availability impact to the vulnerable system. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade Handlebars to version 4.7.10 (vendor-released patch; fixed via commit ceec388abe1d1aac8f6369860d5f390fa71ef4fa and PR 2185, referenced from the advisory at https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-vrv2-v86f and the v4.7.10 release notes). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, inventory every application and service that depends on Handlebars versions 4.0.0 through 4.7.9, confirm whether the non-default allowProtoMethodsByDefault option is enabled anywhere, and where possible disable it or restrict template rendering to trusted, developer-controlled sources to close the known exploitation preconditions; treat any service that renders attacker-controlled template source with that option enabled as the top priority. …
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External POC / Exploit Code
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