Vulnerability Details CVE-2026-33916
Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `resolvePartial()` in the Handlebars runtime resolves partial names via a plain property lookup on `options.partials` without guarding against prototype-chain traversal. When `Object.prototype` has been polluted with a string value whose key matches a partial reference in a template, the polluted string is used as the partial body and rendered without HTML escaping, resulting in reflected or stored XSS. Version 4.7.9 fixes the issue. Some workarounds are available. Apply `Object.freeze(Object.prototype)` early in application startup to prevent prototype pollution. Note: this may break other libraries, and/or use the Handlebars runtime-only build (`handlebars/runtime`), which does not compile templates and reduces the attack surface.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 8.3%
CVSS Severity
CVSS v3 Score 4.7
References
Products affected by CVE-2026-33916
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cpe:2.3:a:handlebarsjs:handlebars:4.0.0
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cpe:2.3:a:handlebarsjs:handlebars:4.0.1
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cpe:2.3:a:handlebarsjs:handlebars:4.0.10
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cpe:2.3:a:handlebarsjs:handlebars:4.0.11
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cpe:2.3:a:handlebarsjs:handlebars:4.0.12
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cpe:2.3:a:handlebarsjs:handlebars:4.0.13
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cpe:2.3:a:handlebarsjs:handlebars:4.0.13-0
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cpe:2.3:a:handlebarsjs:handlebars:4.0.14
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cpe:2.3:a:handlebarsjs:handlebars:4.0.2
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cpe:2.3:a:handlebarsjs:handlebars:4.0.3
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cpe:2.3:a:handlebarsjs:handlebars:4.0.4
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cpe:2.3:a:handlebarsjs:handlebars:4.0.5
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cpe:2.3:a:handlebarsjs:handlebars:4.0.6
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cpe:2.3:a:handlebarsjs:handlebars:4.0.7
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cpe:2.3:a:handlebarsjs:handlebars:4.0.8
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cpe:2.3:a:handlebarsjs:handlebars:4.0.9
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cpe:2.3:a:handlebarsjs:handlebars:4.1.0
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cpe:2.3:a:handlebarsjs:handlebars:4.1.1
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cpe:2.3:a:handlebarsjs:handlebars:4.1.2
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cpe:2.3:a:handlebarsjs:handlebars:4.1.2-0
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cpe:2.3:a:handlebarsjs:handlebars:4.2.0
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cpe:2.3:a:handlebarsjs:handlebars:4.2.1
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cpe:2.3:a:handlebarsjs:handlebars:4.2.2
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cpe:2.3:a:handlebarsjs:handlebars:4.3.0
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cpe:2.3:a:handlebarsjs:handlebars:4.3.1
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cpe:2.3:a:handlebarsjs:handlebars:4.3.2
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cpe:2.3:a:handlebarsjs:handlebars:4.3.3
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cpe:2.3:a:handlebarsjs:handlebars:4.3.4
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cpe:2.3:a:handlebarsjs:handlebars:4.3.5
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cpe:2.3:a:handlebarsjs:handlebars:4.4.0
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cpe:2.3:a:handlebarsjs:handlebars:4.4.1
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cpe:2.3:a:handlebarsjs:handlebars:4.4.2
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cpe:2.3:a:handlebarsjs:handlebars:4.4.3
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cpe:2.3:a:handlebarsjs:handlebars:4.4.4
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cpe:2.3:a:handlebarsjs:handlebars:4.4.5
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cpe:2.3:a:handlebarsjs:handlebars:4.5.0
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cpe:2.3:a:handlebarsjs:handlebars:4.5.1
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cpe:2.3:a:handlebarsjs:handlebars:4.5.2
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cpe:2.3:a:handlebarsjs:handlebars:4.5.3
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cpe:2.3:a:handlebarsjs:handlebars:4.6.0
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cpe:2.3:a:handlebarsjs:handlebars:4.7.0
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cpe:2.3:a:handlebarsjs:handlebars:4.7.1
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cpe:2.3:a:handlebarsjs:handlebars:4.7.2
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cpe:2.3:a:handlebarsjs:handlebars:4.7.3
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cpe:2.3:a:handlebarsjs:handlebars:4.7.4
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cpe:2.3:a:handlebarsjs:handlebars:4.7.5
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cpe:2.3:a:handlebarsjs:handlebars:4.7.6
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cpe:2.3:a:handlebarsjs:handlebars:4.7.7