CVE-2026-33940 | Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial

Exp

Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, a crafted object placed in the template context can bypass all conditional guards in `resolvePartial()` and cause `invokePartial()` to return `undefined`. The Handlebars runtime then treats the unresolved partial as a source that needs to be compiled, passing the crafted object to `env.compile()`. Because the object is a valid Handlebars AST containing injected code, the generated JavaScript executes arbitrary commands on the server. The attack requires the adversary to control a value that can be returned by a dynamic partial lookup. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). Without `compile()`, the fallback compilation path in `invokePartial` is unreachable. Second, sanitize context data before rendering: Ensure no value in the context is a non-primitive object that could be passed to a dynamic partial. Third, avoid dynamic partial lookups (`{{> (lookup ...)}}`) when context data is user-controlled.

Published: 2026-03-27 Last update: 2026-03-31 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-33940 is rated Exploit Available (50/100): CVSS High severity, with low exploitation likelihood (EPSS 0.02%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2026-33940

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2026-33940

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-21 0.06% 0.02% -0.04%
2 2026-04-02 0.04% 0.06% +0.01%
3 2026-03-28 — 0.04% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-33940

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.1 3.1 HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 5.9 [email protected]

Weakness enumeration for CVE-2026-33940

GitHub Security Advisory for CVE-2026-33940

GHSA-xhpv-hc6g-r9c6 · Severity: high · Ecosystem: npm — Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial

OS Trackers for CVE-2026-33940

vendor priority summary link
debian not yet assigned CVE-2026-33940 not yet assigned priority: Debian including 1 source packages (node-handlebars), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 3, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-33940
redhat high — https://access.redhat.com/security/cve/CVE-2026-33940
ubuntu medium CVE-2026-33940 medium priority: Ubuntu including 1 source packages (node-handlebars), 6 status rows across 6 suites (bionic, focal, jammy, noble, questing, upstream): needs-triage 5, released 1. https://ubuntu.com/security/CVE-2026-33940

Affected software / configurations for CVE-2026-33940

Vendor Product Version Raw CPE
handlebarsjs handlebars >= 4.0.0, < 4.7.9 cpe:2.3:a:handlebarsjs:handlebars:*:*:*:*:*:node.js:*:*

References for CVE-2026-33940

cvelogic Threat Intelligence