CVE-2026-33939
Description
A flaw was found in Handlebars.js. A remote attacker can exploit this by submitting a malformed Handlebars template that includes decorator syntax referencing an unregistered decorator. When the application attempts to compile this template without proper error handling, it triggers an unhandled TypeError. This error causes the Node.js process to crash, resulting in a Denial of Service (DoS) for the affected application.
Statement
This is an Important denial of service flaw in Handlebars.js affecting applications that compile user-supplied templates without proper error handling. A remote attacker can submit a malformed template containing unregistered decorator syntax, leading to an unhandled TypeError and crashing the Node.js process. Red Hat products are vulnerable if they use Handlebars.js in a configuration that allows untrusted input to be compiled at runtime without implementing try/catch blocks or input validation.
Mitigation
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.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability,Confidentiality
Technical Impact: DoS: Crash, Exit, or Restart; Read Application Data
An uncaught exception could cause the system to be placed in a state that could lead to a crash, exposure of sensitive information or other unintended behaviors.
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