CVE-2026-33937: Handlebars.js has JavaScript Injection via AST Type Confusion
Description
Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `Handlebars.compile()` accepts a pre-parsed AST object in addition to a template string. The `value` field of a `NumberLiteral` AST node is emitted directly into the generated JavaScript without quoting or sanitization. An attacker who can supply a crafted AST to `compile()` can therefore inject and execute arbitrary JavaScript, leading to Remote Code Execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. Validate input type before calling `Handlebars.compile()`; ensure the argument is always a `string`, never a plain object or JSON-deserialized value. Use the Handlebars runtime-only build (`handlebars/runtime`) on the server if templates are pre-compiled at build time; `compile()` will be unavailable.
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H · CWE-843, CWE-94
Status incidents that name it
- Wiz Some customers may see critical issues created from incorrectly classified vulnerability findings for CVE-2026-4800, CVE-2026-33937, CVE-2026-33938, and CVE-2026-33940· No impact listed · names this CVE
“Some customers may see critical issues created from incorrectly classified vulnerability findings for CVE-2026-4800, CVE-2026-33937, CVE-2026-33938, and CVE-2026-33940 This incident has been resolved. This incident has been resolved. A fix has been…”
Affected vendors and products
handlebars-lang: handlebars.jsRed Hat: Cluster Observability Operator 1.5.0Red Hat: Cryostat 4Red Hat: Logging Subsystem for Red Hat OpenShiftRed Hat: Red Hat Data Grid 8Red Hat: Red Hat Developer HubRed Hat: Red Hat Enterprise Linux 10Red Hat: Red Hat Enterprise Linux 7Red Hat: Red Hat Enterprise Linux 8Red Hat: Red Hat Enterprise Linux 9Red Hat: Red Hat OpenShift AI (RHOAI)Red Hat: Red Hat OpenShift Dev SpacesRed Hat: Red Hat OpenShift Dev Spaces 3.27Red Hat: Red Hat Process Automation 7
References
- CVE record on cve.org (opens in new tab)
- NVD entry (opens in new tab)
- github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe… (opens in new tab)
- github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9 (opens in new tab)
- github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2w6w-674q-4c4q (opens in new tab)
- CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (opens in new tab)
- This product uses data from the NVD API but is not endorsed or certified by the NVD. (opens in new tab)
- Known Exploited Vulnerabilities catalog from CISA. (opens in new tab)
- EPSS scores from FIRST (Exploit Prediction Scoring System). (opens in new tab)