{"id":"CVE-2026-33938","state":"PUBLISHED","title":"Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block","description":"Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, the `@partial-block` special variable is stored in the template data context and is reachable and mutable from within a template via helpers that accept arbitrary objects. When a helper overwrites `@partial-block` with a crafted Handlebars AST, a subsequent invocation of `{{> @partial-block}}` compiles and executes that AST, enabling arbitrary JavaScript execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). The `compile()` method is  absent, eliminating the vulnerable fallback path. Second, audit registered helpers for any that write arbitrary values to context objects. Helpers  should treat context data as read-only. Third, avoid registering helpers from third-party packages (such as `handlebars-helpers`) in  contexts where templates or context data can be influenced by untrusted input.","publishedAt":"2026-03-27T21:05:42.485Z","updatedAt":"2026-09-04T12:04:55.157Z","severity":{"score":8.1,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["handlebars-lang handlebars.js"],"affected":[{"vendor":"handlebars-lang","product":"handlebars.js","versions":[{"version":">= 4.0.0, < 4.7.9","status":"affected"}]}],"references":["https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-3mfm-83xf-c92r","https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2","https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9","https://access.redhat.com/security/cve/CVE-2026-33938","https://bugzilla.redhat.com/show_bug.cgi?id=2452525","https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33938.json","https://access.redhat.com/errata/RHSA-2026:34342","https://access.redhat.com/errata/RHSA-2026:10175"],"weaknesses":["CWE-94","CWE-843","CWE-917"],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/33xxx/CVE-2026-33938.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-33938","state":"PUBLISHED","datePublished":"2026-03-27T21:05:42.485Z","dateUpdated":"2026-09-04T12:04:55.157Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-03-24T19:50:52.103Z"},"containers":{"cna":{"title":"Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block","descriptions":[{"lang":"en","value":"Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, the `@partial-block` special variable is stored in the template data context and is reachable and mutable from within a template via helpers that accept arbitrary objects. When a helper overwrites `@partial-block` with a crafted Handlebars AST, a subsequent invocation of `{{> @partial-block}}` compiles and executes that AST, enabling arbitrary JavaScript execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). The `compile()` method is  absent, eliminating the vulnerable fallback path. Second, audit registered helpers for any that write arbitrary values to context objects. Helpers  should treat context data as read-only. Third, avoid registering helpers from third-party packages (such as `handlebars-helpers`) in  contexts where templates or context data can be influenced by untrusted input."}],"affected":[{"vendor":"handlebars-lang","product":"handlebars.js","versions":[{"version":">= 4.0.0, < 4.7.9","status":"affected"}]}],"references":[{"url":"https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-3mfm-83xf-c92r","name":"https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-3mfm-83xf-c92r","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2","name":"https://github.com/handlebars-lang/handlebars.js/commit/68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2","tags":["x_refsource_MISC"]},{"url":"https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9","name":"https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":8.1,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-94","lang":"en","description":"CWE-94: Improper Control of Generation of Code ('Code Injection')","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-843","lang":"en","description":"CWE-843: Access of Resource Using Incompatible Type ('Type Confusion')","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-03-27T21:05:42.485Z"},"source":{"advisory":"GHSA-3mfm-83xf-c92r","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-3mfm-83xf-c92r","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-03-31T00:00:00+00:00","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3","id":"CVE-2026-33938"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-04-01T03:55:42.796Z"}},{"title":"handlebars: Handlebars: Arbitrary code execution via @partial-block overwrite","descriptions":[{"lang":"en","value":"A flaw was found in Handlebars. A remote attacker can exploit this vulnerability by manipulating the `@partial-block` special variable within the template data context. By overwriting `@partial-block` with a specially crafted Abstract Syntax Tree (AST) through a helper, a subsequent invocation of `{{> @partial-block}}` will compile and execute the malicious AST. 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