Bug 2452508 (CVE-2026-33939)
| Summary: | CVE-2026-33939 handlebars.js: Handlebars.js: Denial of Service via malformed decorator syntax in template compilation | ||
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| Product: | [Other] Security Response | Reporter: | OSIDB Bzimport <bzimport> |
| Component: | vulnerability | Assignee: | Product Security <prodsec-ir-bot> |
| Status: | NEW --- | QA Contact: | |
| Severity: | high | Docs Contact: | |
| Priority: | high | ||
| Version: | unspecified | CC: | aazores, abuckta, cmah, dhanak, dkuc, drosa, eaguilar, ebaron, gotiwari, ibek, jcantril, jgrulich, jhorak, jkoehler, jolong, jrokos, lchilton, lphiri, mnovotny, mvyas, orabin, pjindal, rhel-process-autobot, rojacob, sausingh, sdawley, sfeifer, tpopela, watson-tool-maintainers |
| Target Milestone: | --- | Keywords: | Security |
| Target Release: | --- | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | --- | |
| Doc Text: |
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.
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | Type: | --- | |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
| Bug Depends On: | 2452609, 2452611, 2452626, 2452659, 2452593, 2452599, 2452603, 2452623, 2452629, 2452637, 2452647, 2452650, 2452653, 2452657, 2452661 | ||
| Bug Blocks: | |||
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.