Handlebars.js has Denial of Service via Malformed Decorator Syntax in Template Compilation
Summary
| CVE | CVE-2026-33939 |
|---|---|
| State | PUBLISHED |
| Assigner | GitHub_M |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-03-27 22:16:20 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, when a Handlebars template contains decorator syntax referencing an unregistered decorator (e.g. `{{*n}}`), the compiled template calls `lookupProperty(decorators, "n")`, which returns `undefined`. The runtime then immediately invokes the result as a function, causing an unhandled `TypeError: ... is not a function` that crashes the Node.js process. Any application that compiles user-supplied templates without wrapping the call in a `try/catch` is vulnerable to a single-request Denial of Service. Version 4.7.9 fixes the issue. Some workarounds are available. Wrap compilation and rendering in `try/catch`. Validate template input before passing it to `compile()`; reject templates containing decorator syntax (`{{*...}}`) if decorators are not used in your application. Use the pre-compilation workflow; compile templates at build time and serve only pre-compiled templates; do not call `compile()` at request time. |
Risk And Classification
Primary CVSS: v3.1 7.5 HIGH from ADP
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS: 0.006160000 probability, percentile 0.454850000 (date 2026-07-16)
Problem Types: CWE-754 | CWE-248 | CWE-754 CWE-754: Improper Check for Unusual or Exceptional Conditions | CWE-248 Uncaught Exception
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | ADP | CVSS | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | [email protected] | Secondary | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | Secondary | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | CNA | DECLARED | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 |
|---|---|---|---|
| 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 |
| access.redhat.com/security/cve/CVE-2026-33939 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | 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-9cx6-3... | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | github.com | Exploit, Vendor Advisory |
| bugzilla.redhat.com/show_bug.cgi | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | bugzilla.redhat.com | |
| security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33939.json | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c | security.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 | 2026-03-27T22:01:36.296Z | Reported to Red Hat. |
| ADP | 2026-03-27T21:08:24.664Z | 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: To mitigate this issue, applications utilizing Handlebars.js should implement robust error handling during template compilation and rendering. Specifically, wrap template compilation and rendering calls in `try/catch` blocks to gracefully handle `TypeError` exceptions. Alternatively, validate user-supplied template input to reject decorator syntax (`{{*...}}`) if decorators are not actively used by the application. Employing a pre-compilation workflow, where templates are compiled at build time and only pre-compiled templates are served, can also prevent runtime exploitation. If the application is a service, a restart may be required for changes to take effect.
There are currently no legacy QID mappings associated with this CVE.