{"id":"CVE-2026-41067","revision":null,"records":[{"revision":"54e2a7c25eda4d1480a7cfd0241b270f","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-41067","aliases":[],"title":"Astro: XSS via incomplete `</script>` sanitization in `define:vars` allows case-insensitive and whitespace-based bypass","description":"Astro is a web framework. Prior to 6.1.6, the defineScriptVars function in Astro's server-side rendering pipeline uses a case-sensitive regex /<\\/script>/g to sanitize values injected into inline <script> tags via the define:vars directive. HTML parsers close <script> elements case-insensitively and also accept whitespace or / before the closing >, allowing an attacker to bypass the sanitization with payloads like </Script>, </script >, or </script/> and inject arbitrary HTML/JavaScript. This vulnerability is fixed in 6.1.6.","state":0,"publishedAt":"2026-04-24T16:57:22.94+00:00","modifiedAt":"2026-04-24T18:16:55.536+00:00","affected":[{"ecosystem":"Vendor product","name":"astro","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"withastro\",\n                    \"product\": \"astro\",\n                    \"versions\": [\n                        {\n                            \"version\": \"< 6.1.6\",\n                            \"status\": \"affected\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","score":6.1,"severity":"MEDIUM"}],"references":["https://github.com/withastro/astro/security/advisories/GHSA-j687-52p2-xcff"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-41067","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-41067","identifiers":["CVE-2026-41067"]},"retained":false,"historicalAffected":[]},{"revision":"638d3371a2ab4264825118731035dc2e","observedAt":"2026-11-01T07:05:31.313+00:00","statement":{"source":"euvd","id":"EUVD-2026-25573","aliases":["CVE-2026-41067","GHSA-j687-52p2-xcff"],"title":"Astro is a web framework. Prior to 6.1.6, the defineScriptVars function in Astro's server-side rendering pipeline uses a case-sensitive regex /<\\/script>/g to sanitize values injected into inline <script> tags via the define:vars directive.…","description":"Astro is a web framework. Prior to 6.1.6, the defineScriptVars function in Astro's server-side rendering pipeline uses a case-sensitive regex /<\\/script>/g to sanitize values injected into inline <script> tags via the define:vars directive. HTML parsers close <script> elements case-insensitively and also accept whitespace or / before the closing >, allowing an attacker to bypass the sanitization with payloads like </Script>, </script >, or </script/> and inject arbitrary HTML/JavaScript. This vulnerability is fixed in 6.1.6.","state":0,"publishedAt":null,"modifiedAt":null,"affected":[],"metrics":[{"system":"EUVD CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","score":6.1,"severity":null}],"references":["https://github.com/withastro/astro/security/advisories/GHSA-j687-52p2-xcff"],"sourceUrl":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-25573","license":"ENISA EUVD · source terms and attribution apply","enrichment":{"sourceStatus":null,"weaknesses":[],"productCriteria":[],"sourceDates":{"datePublished":"Apr 24, 2026, 4:57:22 PM","dateUpdated":"Apr 24, 2026, 6:16:55 PM"},"relatedAdvisories":[],"note":"EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON."},"key":"euvd:EUVD-2026-25573","identifiers":["EUVD-2026-25573","CVE-2026-41067","GHSA-j687-52p2-xcff"]},"retained":false,"historicalAffected":[]},{"revision":"4b157f9b4a6b4250998467ab3cd56ddd","observedAt":"2026-10-27T10:10:07.342+00:00","statement":{"source":"nvd","id":"CVE-2026-41067","aliases":[],"title":"Astro is a web framework. Prior to 6.1.6, the defineScriptVars function in Astro's server-side rendering pipeline uses a case-sensitive regex /<\\/script>/g to sanitize values injected into inline <script> tags via the define:vars directive.…","description":"Astro is a web framework. Prior to 6.1.6, the defineScriptVars function in Astro's server-side rendering pipeline uses a case-sensitive regex /<\\/script>/g to sanitize values injected into inline <script> tags via the define:vars directive. HTML parsers close <script> elements case-insensitively and also accept whitespace or / before the closing >, allowing an attacker to bypass the sanitization with payloads like </Script>, </script >, or </script/> and inject arbitrary HTML/JavaScript. This vulnerability is fixed in 6.1.6.","state":0,"publishedAt":"2026-04-24T17:16:21.083+00:00","modifiedAt":"2026-10-26T22:10:00.163+00:00","affected":[],"metrics":[{"system":"CVSS 3.1 · security-advisories@github.com · Secondary","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","score":6.1,"severity":"MEDIUM"}],"references":["https://github.com/withastro/astro/security/advisories/GHSA-j687-52p2-xcff"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-41067","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Analyzed","weaknesses":["CWE-79"],"productCriteria":["cpe:2.3:a:astro:astro:*:*:*:*:*:node.js:*:*"],"sourceDates":{"published":"2026-04-24T17:16:21.083","lastModified":"2026-10-26T22:10:00.163"},"relatedAdvisories":[],"note":"NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-41067","identifiers":["CVE-2026-41067"]},"retained":false,"historicalAffected":[]},{"revision":"a9fdd9f16ef94372abd5da18acaeaa28","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-j687-52p2-xcff","aliases":["CVE-2026-41067"],"title":"Astro: XSS in define:vars via incomplete </script> tag sanitization","description":"## Summary\n\nThe `defineScriptVars` function in Astro's server-side rendering pipeline uses a case-sensitive regex `/<\\/script>/g` to sanitize values injected into inline `<script>` tags via the `define:vars` directive. HTML parsers close `<script>` elements case-insensitively and also accept whitespace or `/` before the closing `>`, allowing an attacker to bypass the sanitization with payloads like `</Script>`, `</script >`, or `</script/>` and inject arbitrary HTML/JavaScript.\n\n## Details\n\nThe vulnerable function is `defineScriptVars` at `packages/astro/src/runtime/server/render/util.ts:42-53`:\n\n```typescript\nexport function defineScriptVars(vars: Record<any, any>) {\n\tlet output = '';\n\tfor (const [key, value] of Object.entries(vars)) {\n\t\toutput += `const ${toIdent(key)} = ${JSON.stringify(value)?.replace(\n\t\t\t/<\\/script>/g,       // ← Case-sensitive, exact match only\n\t\t\t'\\\\x3C/script>',\n\t\t)};\\n`;\n\t}\n\treturn markHTMLString(output);\n}\n```\n\nThis function is called from `renderElement` at `util.ts:172-174` when a `<script>` element has `define:vars`:\n\n```typescript\nif (name === 'script') {\n\tdelete props.hoist;\n\tchildren = defineScriptVars(defineVars) + '\\n' + children;\n}\n```\n\nThe regex `/<\\/script>/g` fails to match three classes of closing script tags that HTML parsers accept per the [HTML specification §13.2.6.4](https://html.spec.whatwg.org/multipage/parsing.html#parsing-main-inbody):\n\n1. **Case variations**: `</Script>`, `</SCRIPT>`, `</sCrIpT>` — HTML tag names are case-insensitive but the regex has no `i` flag.\n2. **Whitespace before `>`**: `</script >`, `</script\\t>`, `</script\\n>` — after the tag name, the HTML tokenizer enters the \"before attribute name\" state on ASCII whitespace.\n3. **Self-closing slash**: `</script/>` — the tokenizer enters \"self-closing start tag\" state on `/`.\n\n`JSON.stringify()` does not escape `<`, `>`, or `/` characters, so all these payloads pass through serialization unchanged.\n\n**Execution flow:** User-controlled input (e.g., `Astro.url.searchParams`) → assigned to a variable → passed via `define:vars` on a `<script>` tag → `renderElement` → `defineScriptVars` → incomplete sanitization → injected into `<script>` block in HTML response → browser closes the script element early → attacker-controlled HTML parsed and executed.\n\n## PoC\n\n**Step 1:** Create an SSR Astro page (`src/pages/index.astro`):\n\n```astro\n---\nconst name = Astro.url.searchParams.get('name') || 'World';\n---\n<html>\n<body>\n  <h1>Hello</h1>\n  <script define:vars={{ name }}>\n    console.log(name);\n  </script>\n</body>\n</html>\n```\n\n**Step 2:** Ensure SSR is enabled in `astro.config.mjs`:\n\n```js\nexport default defineConfig({\n  output: 'server'\n});\n```\n\n**Step 3:** Start the dev server and visit:\n\n```\nhttp://localhost:4321/?name=</Script><img/src=x%20onerror=alert(document.cookie)>\n```\n\n**Step 4:** View the HTML source. The output contains:\n\n```html\n<script>const name = \"</Script><img/src=x onerror=alert(document.cookie)>\";\n  console.log(name);\n</script>\n```\n\nThe browser's HTML parser matches `</Script>` case-insensitively, closing the script block. The `<img onerror=alert(document.cookie)>` is then parsed as HTML and the JavaScript in `onerror` executes.\n\n**Alternative bypass payloads:**\n\n```\n/?name=</script ><img/src=x onerror=alert(1)>\n/?name=</script/><img/src=x onerror=alert(1)>\n/?name=</SCRIPT><img/src=x onerror=alert(1)>\n```\n\n## Impact\n\nAn attacker can execute arbitrary JavaScript in the context of a victim's browser session on any SSR Astro application that passes request-derived data to `define:vars` on a `<script>` tag. This is a documented and expected usage pattern in Astro.\n\nExploitation enables:\n- **Session hijacking** via cookie theft (`document.cookie`)\n- **Credential theft** by injecting fake login forms or keyloggers\n- **Defacement** of the rendered page\n- **Redirection** to attacker-controlled domains\n\nThe vulnerability affects all Astro versions that support `define:vars` and is exploitable in any SSR deployment where user input reaches a `define:vars` script variable.\n\n## Recommended Fix\n\nReplace the case-sensitive exact-match regex with a comprehensive escape that covers all HTML parser edge cases. The simplest correct fix is to escape all `<` characters in the JSON output:\n\n```typescript\nexport function defineScriptVars(vars: Record<any, any>) {\n\tlet output = '';\n\tfor (const [key, value] of Object.entries(vars)) {\n\t\toutput += `const ${toIdent(key)} = ${JSON.stringify(value)?.replace(\n\t\t\t/</g,\n\t\t\t'\\\\u003c',\n\t\t)};\\n`;\n\t}\n\treturn markHTMLString(output);\n}\n```\n\nThis is the standard approach used by frameworks like Next.js and Rails. Replacing every `<` with `\\u003c` is safe inside JSON string contexts (JavaScript treats `\\u003c` as `<` at runtime) and eliminates all possible `</script>` variants including case variations, whitespace, and self-closing forms.","state":0,"publishedAt":"2026-04-21T20:39:49+00:00","modifiedAt":"2026-05-05T16:07:54.66086+00:00","affected":[{"ecosystem":"npm","name":"astro","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"6.1.6"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"MODERATE"}],"references":["https://github.com/withastro/astro/security/advisories/GHSA-j687-52p2-xcff","https://nvd.nist.gov/vuln/detail/CVE-2026-41067","https://github.com/withastro/astro","https://github.com/withastro/astro/releases/tag/astro@6.1.6"],"sourceUrl":"https://github.com/advisories/GHSA-j687-52p2-xcff","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-j687-52p2-xcff","identifiers":["GHSA-j687-52p2-xcff","CVE-2026-41067"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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