Widely-used Handlebars template library; RCE in server code could disrupt many apps/infrastructure.
CVE-2026-33937
RCE via crafted AST in Handlebars.compile() (v4.0.0–4.7.8); fixed in 4.7.9.
Is CVE-2026-33937 being exploited?
Not confirmed. CVE-2026-33937 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 1.7% probability of exploitation in the next 30 days.
How severe is CVE-2026-33937?
CVE-2026-33937 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-33937?
Yes. A fix has been recorded for CVE-2026-33937. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-33937 affect?
CVE-2026-33937 affects Handlebars.js (v4.0.0–4.7.8). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-33937?
Upgrade to 4.7.9+; validate input types; use runtime-only build on server.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution on server via crafted AST injected into compile(); attacker-controlled JavaScript executes.
Immediate action required
- affected>= 4.0.0 and < 4.7.9
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.