Read the docs
TI-2026-26289 Aliases CVE-2026-33938GHSA-3mfm-83xf-c92r

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

Priority HIGH 70CWE-843Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Impact type
Code execution
Confidentiality · integrity · availability
High · High · High
Fix status
Partial Red Hat: 2 fixed, 3 without a fix

Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-843 and the CVSS impact.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00721 54th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Partial handlebars.js (handlebars-lang): 4.7.9handlebars (npm): 4.7.9Red Hat: 2 advisoriesRed Hat: 2 fixed, 3 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
handlebars-langhandlebars.js4.0.0 to before 4.7.94.7.9Patch availableCNA
—handlebars (npm)4.0.0 to before 4.7.94.7.9Patch availableGHSA-3mfm-83xf-c92r
  • handlebars.js Vendorhandlebars-lang Affected 4.0.0 to before 4.7.9 Fixed in 4.7.9 Patch available CNA
  • handlebars (npm) Vendor— Affected 4.0.0 to before 4.7.9 Fixed in 4.7.9 Patch available GHSA-3mfm-83xf-c92r

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:handlebarsjs:handlebars:*:*:*:*:*:node.js:*:*4.0.0 to before 4.7.9Vulnerablehandlebars-lang
  • cpe:2.3:a:handlebarsjs:handlebars:*:*:*:*:*:node.js:*:* Versions 4.0.0 to before 4.7.9 Vulnerable ·handlebars-lang

Remediation

  • Fix · CNA handlebars.js (handlebars-lang) Fixed in 4.7.9
  • Fix · GHSA-3mfm-83xf-c92r handlebars (npm) Fixed in 4.7.9 Advisory →

Red Hat 2 advisories

  • RHSA-2026:34342 Released 2026-07-01 · Red Hat rating Critical
    Cluster Observability Operator 1.5.0
    • Cluster Observability Operator 1.5 registry.redhat.io/cluster-observability-operator/distributed-tracing-console-plugin-pf4-rhel9, registry.redhat.io/cluster-observability-operator/distributed-tracing-console-plugin-pf5-rhel9, registry.redhat.io/cluster-observability-operator/distributed-tracing-console-plugin-pf6-rhel9 +9
  • RHSA-2026:10175 Released 2026-04-23 · Red Hat rating Important
    Red Hat OpenShift Dev Spaces 3.27.1 Release.
    • Red Hat OpenShift Dev Spaces 3.27 registry.redhat.io/devspaces/code-rhel9, registry.redhat.io/devspaces/dashboard-rhel9, registry.redhat.io/devspaces/devspaces-rhel9-operator +8

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
Logging Subsystem for Red Hat OpenShiftAffectedNo fix planned: Will not fix
Red Hat Developer Hub 1AffectedNo fix yet
Red Hat Enterprise Linux 8AffectedNo fix planned: Will not fix
Cluster Observability Operator 1.5Fixed RHSA-2026:34342
Red Hat OpenShift Dev Spaces 3.27Fixed RHSA-2026:10175
Not affected: 11 products
  • Cluster Observability Operator 1.5
  • Cryostat 4
  • Red Hat Data Grid 8
  • Red Hat Enterprise Linux 10
  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 9
  • Red Hat OpenShift AI (RHOAI)
  • Red Hat OpenShift Dev Spaces
  • Red Hat OpenShift Dev Spaces 3.27
  • Red Hat Process Automation 7

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-33938
  2. 2026-10-03 Alias added: GHSA-3mfm-83xf-c92r
  3. 2026-10-18 Fix available: Cluster Observability Operator 1.5.3 · Red Hat
  4. 2026-10-27 Affected versions changed · Red Hat
  5. 2026-11-05 Fix available: Cluster Observability Operator 1.5 · Red Hat

References

Exploit 1

Patch 1

Advisory 1

Other 2

  • TI-2026-26288 Handlebars.js has JavaScript Injection via AST Type Confusion CVSS 3.1CRITICAL 9.8
  • TI-2026-26290 Handlebars.js has Denial of Service via Malformed Decorator Syntax in Template Compilation CVSS 3.1HIGH 7.5
  • TI-2026-26292 Handlebars.js has JavaScript Injection in CLI Precompiler via Unescaped Names and Options CVSS 3.1HIGH 8.3
  • TI-2026-26291 Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial CVSS 3.1HIGH 8.1
  • TI-2021-06062 Remote code execution (RCE) in handlebars CVSS 3.1CRITICAL 9.8
  • TI-2021-06076 Prototype pollution in handlebars CVSS 3.1CRITICAL 9.8
See all 9 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences