Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block
Summary
| CVE | CVE-2026-33938 |
|---|---|
| State | PUBLISHED |
| Assigner | GitHub_M |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-03-27 21:17:27 UTC |
| Updated | 2026-07-15 02:20:23 UTC |
| Description | 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. |
Risk And Classification
Primary CVSS: v3.1 8.1 HIGH from ADP
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS: 0.007090000 probability, percentile 0.493380000 (date 2026-07-16)
Problem Types: CWE-94 | CWE-843 | CWE-917 | CWE-94 CWE-94: Improper Control of Generation of Code ('Code Injection') | CWE-843 CWE-843: Access of Resource Using Incompatible Type ('Type Confusion') | CWE-917 Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | ADP | CVSS | 8.1 | HIGH | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H |
| 3.1 | [email protected] | Secondary | 8.1 | HIGH | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H |
| 3.1 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | Secondary | 8.1 | HIGH | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H |
| 3.1 | CNA | DECLARED | 8.1 | HIGH | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
HighPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
HighIntegrity
HighAvailability
HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD Known Affected Configurations (CPE 2.3)
| Type | Vendor | Product | Version | Update | Edition | Language |
|---|---|---|---|---|---|---|
| Application | Handlebarsjs | Handlebars | All | All | All | All |
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Handlebars-lang | Handlebars.js | affected >= 4.0.0, < 4.7.9 | Not specified |
| ADP | Red Hat | Cluster Observability Operator 1.5.0 | unaffected 1782839279 * rpm | Not specified |
| ADP | Red Hat | Cluster Observability Operator 1.5.0 | unaffected 1782840539 * rpm | Not specified |
| ADP | Red Hat | Cluster Observability Operator 1.5.0 | unaffected 1782839996 * rpm | Not specified |
| ADP | Red Hat | Red Hat OpenShift Dev Spaces 3.27 | unaffected 1776744110 * rpm | Not specified |
| ADP | Red Hat | Cryostat 4 | Not specified | Not specified |
| ADP | Red Hat | Logging Subsystem For Red Hat OpenShift | Not specified | Not specified |
| ADP | Red Hat | Logging Subsystem For Red Hat OpenShift | Not specified | Not specified |
| ADP | Red Hat | Logging Subsystem For Red Hat OpenShift | Not specified | Not specified |
| ADP | Red Hat | Logging Subsystem For Red Hat OpenShift | Not specified | Not specified |
| ADP | Red Hat | Logging Subsystem For Red Hat OpenShift | Not specified | Not specified |
| ADP | Red Hat | Logging Subsystem For Red Hat OpenShift | Not specified | Not specified |
| ADP | Red Hat | Red Hat Data Grid 8 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 10 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 10 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 7 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 8 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 8 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 8 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 8 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 8 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 9 | Not specified | Not specified |
| ADP | Red Hat | Red Hat Enterprise Linux 9 | Not specified | Not specified |
| ADP | Red Hat | Red Hat OpenShift AI RHOAI | Not specified | Not specified |
| ADP | Red Hat | Red Hat Process Automation 7 | Not specified | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| bugzilla.redhat.com/show_bug.cgi | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | bugzilla.redhat.com | |
| access.redhat.com/errata/RHSA-2026:34342 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9 | [email protected] | github.com | Release Notes |
| security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33938.json | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | security.access.redhat.com | |
| access.redhat.com/errata/RHSA-2026:10175 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c... | [email protected] | github.com | Patch |
| github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-3mfm-8... | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | github.com | Exploit, Vendor Advisory |
| access.redhat.com/security/cve/CVE-2026-33938 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | access.redhat.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
Additional Advisory Data
| Source | Time | Event |
|---|---|---|
| ADP | 2026-03-27T22:02:58.504Z | Reported to Red Hat. |
| ADP | 2026-03-27T21:05:42.485Z | Made public. |
Solutions
ADP: RHSA-2026:34342: Cluster Observability Operator 1.5.0
ADP: RHSA-2026:10175: Red Hat OpenShift Dev Spaces 3.27
Workarounds
ADP: Applications using Handlebars should implement the runtime-only build (`require('handlebars/runtime')`) to prevent exploitation, as this build lacks the vulnerable `compile()` method. Additionally, review all registered helpers to ensure they do not write arbitrary values to context objects, and avoid using third-party helpers in contexts exposed to untrusted input.
There are currently no legacy QID mappings associated with this CVE.