CVE-2026-33938 | Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block

Exp

Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, the `@partial-block` special variable is stored in the template data context and is reachable and mutable from within a template via helpers that accept arbitrary objects. When a helper overwrites `@partial-block` with a crafted Handlebars AST, a subsequent invocation of `{{> @partial-block}}` compiles and executes that AST, enabling arbitrary JavaScript execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). The `compile()` method is absent, eliminating the vulnerable fallback path. Second, audit registered helpers for any that write arbitrary values to context objects. Helpers should treat context data as read-only. Third, avoid registering helpers from third-party packages (such as `handlebars-helpers`) in contexts where templates or context data can be influenced by untrusted input.

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

CVE-2026-33938 is rated Exploit Available (50.5/100): CVSS High severity, with low exploitation likelihood (EPSS 0.03%). 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-2026-33938

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

Exploit prediction scoring system (EPSS) score for CVE-2026-33938

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 0.07% 0.03% -0.04%
2 2026-03-28 — 0.07% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-33938

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-2026-33938

GitHub Security Advisory for CVE-2026-33938

GHSA-3mfm-83xf-c92r · Severity: high · Ecosystem: npm — Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block

OS Trackers for CVE-2026-33938

vendor priority summary link
debian not yet assigned CVE-2026-33938 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-2026-33938
redhat high — https://access.redhat.com/security/cve/CVE-2026-33938
ubuntu medium CVE-2026-33938 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-2026-33938

Affected software / configurations for CVE-2026-33938

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

References for CVE-2026-33938

cvelogic Threat Intelligence