CVE-2026-33938 (GCVE-0-2026-33938)
Vulnerability from cvelistv5 – Published: 2026-03-27 21:05 – Updated: 2026-09-04 12:04
VLAI
EPSS
VEX
Title
Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block
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.
Severity
8.1 (High)
SSVC
Exploitation: poc
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-03-31 00:00 UTC
CWE
Assigner
References
8 references
| URL | Tags |
|---|---|
| https://github.com/handlebars-lang/handlebars.js/… | x_refsource_CONFIRM |
| https://github.com/handlebars-lang/handlebars.js/… | x_refsource_MISC |
| https://github.com/handlebars-lang/handlebars.js/… | x_refsource_MISC |
| https://access.redhat.com/security/cve/CVE-2026-33938 | vdb-entryx_refsource_REDHAT |
| https://bugzilla.redhat.com/show_bug.cgi?id=2452525 | issue-trackingx_refsource_REDHAT |
| https://security.access.redhat.com/data/csaf/v2/v… | x_sadp-csaf-vex |
| https://access.redhat.com/errata/RHSA-2026:34342 | vendor-advisoryx_refsource_REDHAT |
| https://access.redhat.com/errata/RHSA-2026:10175 | vendor-advisoryx_refsource_REDHAT |
Impacted products
16 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| handlebars-lang | handlebars.js |
Affected:
>= 4.0.0, < 4.7.9
|
guessed | |
| Red Hat | Cluster Observability Operator 1.5.0 |
Unaffected:
1782839279 , < *
(rpm)
cpe:/a:redhat:cluster_observability_operator:1.5::el9 |
||
| Red Hat | Cluster Observability Operator 1.5.0 |
Unaffected:
1782840539 , < *
(rpm)
cpe:/a:redhat:cluster_observability_operator:1.5::el9 |
||
| Red Hat | Cluster Observability Operator 1.5.0 |
Unaffected:
1782839996 , < *
(rpm)
cpe:/a:redhat:cluster_observability_operator:1.5::el9 |
||
| Red Hat | Red Hat OpenShift Dev Spaces 3.27 |
Unaffected:
1776744110 , < *
(rpm)
cpe:/a:redhat:openshift_devspaces:3.27::el9 |
||
| Red Hat | Cryostat 4 |
cpe:/a:redhat:cryostat:4
|
||
| Red Hat | Logging Subsystem for Red Hat OpenShift |
cpe:/a:redhat:logging:5
|
||
| Red Hat | Red Hat Data Grid 8 |
cpe:/a:redhat:jboss_data_grid:8
|
||
| Red Hat | Red Hat Developer Hub |
cpe:/a:redhat:rhdh:1
|
||
| Red Hat | Red Hat Enterprise Linux 10 |
cpe:/o:redhat:enterprise_linux:10
|
||
| Red Hat | Red Hat Enterprise Linux 7 |
cpe:/o:redhat:enterprise_linux:7
|
||
| Red Hat | Red Hat Enterprise Linux 8 |
cpe:/o:redhat:enterprise_linux:8
|
||
| Red Hat | Red Hat Enterprise Linux 9 |
cpe:/o:redhat:enterprise_linux:9
|
||
| Red Hat | Red Hat OpenShift AI (RHOAI) |
cpe:/a:redhat:openshift_ai
|
||
| Red Hat | Red Hat OpenShift Dev Spaces |
cpe:/a:redhat:openshift_devspaces:3
|
||
| Red Hat | Red Hat Process Automation 7 |
cpe:/a:redhat:jboss_enterprise_bpms_platform:7
|
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"value": "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 `{{\u003e @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(\u0027handlebars/runtime\u0027)`). 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."
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"value": "Handlebars proporciona la potencia necesaria para permitir a los usuarios construir plantillas sem\u00e1nticas. En las versiones 4.0.0 a 4.7.8, la variable especial \u201c@partial-block\u201d se almacena en el contexto de datos de la plantilla y es accesible y mutable desde dentro de una plantilla a trav\u00e9s de helpers que aceptan objetos arbitrarios. Cuando un helper sobrescribe \u201c@partial-block\u201d con un AST de Handlebars manipulado, una invocaci\u00f3n posterior de \u201c{{\u003e @partial-block}}\u201d compila y ejecuta ese AST, permitiendo la ejecuci\u00f3n arbitraria de JavaScript en el servidor. La versi\u00f3n 4.7.9 corrige el problema. Hay algunas soluciones alternativas disponibles. Primero, use la compilaci\u00f3n solo en tiempo de ejecuci\u00f3n (\u201crequire(\u2019handlebars/runtime\u2019)\u201d). El m\u00e9todo \u201ccompile()\u201d est\u00e1 ausente, eliminando la ruta de reserva vulnerable. Segundo, audite los helpers registrados en busca de cualquiera que escriba valores arbitrarios en objetos de contexto. Los helpers deben tratar los datos de contexto como de solo lectura. Tercero, evite registrar helpers de paquetes de terceros (como \u201chandlebars-helpers\u201d) en contextos donde las plantillas o los datos de contexto puedan ser influenciados por entradas no confiables."
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.