GHSA-g2v6-rqmx-r4w6

@vue/server-renderer: XSS via missing CR in attribute-name blacklist

Published

2026-10-05

Modified

2026-10-05

Sources

github-advisory

Summary

## Description `@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. `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: ```ts export function ssrRenderDynamicAttr( key: string, value: unknown, tag?: string, ): string { if (!isRenderableAttrValue(value)) { return `` } const attrKey = ... if (isBooleanAttr(attrKey) || ...) { return includeBooleanAttr(value) ? ` ${attrKey}` : `` } else if (isSSRSafeAttrName(attrKey)) { return value === '' ? ` ${attrKey}` : ` ${attrKey}="${escapeHtml(value)}"` } else { console.warn(`[@vue/server-renderer] Skipped rendering unsafe attribute name: ${attrKey}`) return `` } } ``` The 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: ```ts // packages/shared/src/domAttrConfig.ts const unsafeAttrCharRE = /[>/="'\u0009\u000a\u000c\u0020]/ export function isSSRSafeAttrName(name: string): boolean { if (attrValidationCache.hasOwnProperty(name)) { return attrValidationCache[name] } const isUnsafe = unsafeAttrCharRE.test(name) if (isUnsafe) { console.error(`unsafe attribute name: ${name}`) } return (attrValidationCache[name] = !isUnsafe) } ``` That blacklist covers: `>`, `/`, `=`, `"`, apostrophe, tab (U+0009), line feed (U+000A), form feed (U+000C), and space (U+0020). It does not cover U+000D -- carriage return (CR, written as `\r` in JS). That matters because of how browsers actually parse HTML. Per the WHATWG HTML parsing spec, the very first step ("preprocessing the input stream") converts every `\r` not followed by `\n` into a `\n` before the tokenizer even starts. So a raw `\r` sitting inside what Vue intends as a single attribute name gets turned into a real line feed by the browser -- and a line feed is one of the characters that terminates an attribute name and starts a new one. The blacklist checks the string as Vue sees it before the browser gets to reinterpret it, and that's exactly the gap. Below is a fresh clone of this repo, confirming the exact commit, the exact vulnerable line, and zero modification to the source: ## Prrof The real, unmodified ssrRenderAttrs() from the published @vue/[email protected] package was tested. The source at HEAD and the upcoming v3.6.0-rc.2 tag were also checked, and the same vulnerable regular expression was present in both; no branch containing a fix was identified. Full script, saved as `poc.mjs` (GitHub doesn't let me attach `.mjs` directly, so the complete file is here): ```js import { ssrRenderAttrs } from '@vue/server-renderer'; import { parseFragment } from 'parse5'; // This is exactly what compiled SSR output calls for ` ` // -- the real, unmodified, published ssrRenderAttrs function. // Full attack chain: the key itself contains ONLY letters, digits, and a // bare \r (carriage return) -- no '>', '/', '=', '"', "'", tab, LF, FF, or // space anywhere, so isSSRSafeAttrName() considers it fully safe. The value // is attacker-controlled JavaScript, delivered as the genuine value of the // LAST \r-separated fragment, which Vue's own template naturally appends via // `="${escapeHtml(value)}"` immediately after the key. const maliciousKey = 'x\rautofocus\ronfocus';

Affected packages

Remediation: Upgrade to 3.5.42 or later.

References

• https://github.com/advisories/GHSA-g2v6-rqmx-r4w6