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Review reviewHigh

CVE-2026-33938

handlebars-lang handlebars.js, Cluster Observability Operator 1.5.0, Red Hat OpenShift Dev Spaces 3.27

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 (`requ...

CVSS
8.1
EPSS
0.71%
50.0% percentile
CISA KEV
Not listed
Published
2026.03.28
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.71%
Technical severityCVSS 8.1

Vulnerability overview

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 (`requ...

Affected product and versions

Product
handlebars-lang handlebars.js, Cluster Observability Operator 1.5.0, Red Hat OpenShift Dev Spaces 3.27
Affected versions
>= >= 4.0.0, < 4.7.9, >= 4.0.0 < 4.7.9
Fixed versions
4.7.9

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that handlebars-lang handlebars.js, Cluster Observability Operator 1.5.0, Red Hat OpenShift Dev Spaces 3.27 and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE
CWE-843, CWE-917, CWE-94