ghsa-j82m-pc2v-2484
Vulnerability from github
Summary
An unsafe parsing logic of the URL from markdown can lead to arbitrary JavaScript code due to a bypass to the existing guards around the javascript: protocol scheme in the URL.
Details
The parsing logic implement at https://github.com/nuxt-modules/mdc/blob/main/src/runtime/parser/utils/props.ts#L16 maintains a deny-list approach to filtering potential malicious payload. It does so by matching protocol schemes like javascript: and others.
Specifically, this is the code from the mdc library's parser that is not secure enough:
```js export const unsafeLinkPrefix = [ 'javascript:', 'data:text/html', 'vbscript:', 'data:text/javascript', 'data:text/vbscript', 'data:text/css', 'data:text/plain', 'data:text/xml' ]
export const validateProp = (attribute: string, value: string) => { if (attribute.startsWith('on')) { return false }
if (attribute === 'href' || attribute === 'src') { return !unsafeLinkPrefix.some(prefix => value.toLowerCase().startsWith(prefix)) }
return true } ```
These security guards can be bypassed by an adversarial that provides JavaScript URLs with HTML entities encoded via hex string.
PoC
The following URL payloads if provided to the markdown parsing library (such as through the usage of import { parseMarkdown } from '@nuxtjs/mdc/runtime';) will trigger the alert() dialog:
```markdown
✅ This is correctly escaped by the parser
- XSS Attempt:
❌ These are vulnerable and not escaped
- Bypass 1:
- Bypass 2:
- Bypass 3:
Click Me 3 ```
Impact
Users who consume this library and perform markdown parsing from unvalidated sources such as LLM generative text responses, user input and other untrusted sources could result in rendering vulnerable XSS anchor links.
Reference
You may infer the following write-up for more in-depth walkthrough of URL parsing problems and suggestions on how to securely address them: How to Parse URLs from Markdown to HTML Securely?
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 0.13.2"
},
"package": {
"ecosystem": "npm",
"name": "@nuxtjs/mdc"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.13.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2025-24981"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": true,
"github_reviewed_at": "2025-02-06T17:16:27Z",
"nvd_published_at": "2025-02-06T18:15:32Z",
"severity": "CRITICAL"
},
"details": "### Summary\nAn unsafe parsing logic of the URL from markdown can lead to arbitrary JavaScript code due to a bypass to the existing guards around the `javascript:` protocol scheme in the URL.\n\n### Details\n\nThe parsing logic implement at [https://github.com/nuxt-modules/mdc/blob/main/src/runtime/parser/utils/props.ts#L16](https://github.com/nuxt-modules/mdc/blob/main/src/runtime/parser/utils/props.ts#L16) maintains a deny-list approach to filtering potential malicious payload. It does so by matching protocol schemes like `javascript:` and others.\n\nSpecifically, this is the code from the mdc library\u0027s parser that is not secure enough:\n\n```js\nexport const unsafeLinkPrefix = [\n \u0027javascript:\u0027,\n \u0027data:text/html\u0027,\n \u0027vbscript:\u0027,\n \u0027data:text/javascript\u0027,\n \u0027data:text/vbscript\u0027,\n \u0027data:text/css\u0027,\n \u0027data:text/plain\u0027,\n \u0027data:text/xml\u0027\n]\n\nexport const validateProp = (attribute: string, value: string) =\u003e {\n if (attribute.startsWith(\u0027on\u0027)) {\n return false\n }\n\n if (attribute === \u0027href\u0027 || attribute === \u0027src\u0027) {\n return !unsafeLinkPrefix.some(prefix =\u003e value.toLowerCase().startsWith(prefix))\n }\n\n return true\n}\n```\n\nThese security guards can be bypassed by an adversarial that provides JavaScript URLs with HTML entities encoded via hex string.\n\n### PoC\n\nThe following URL payloads if provided to the markdown parsing library (such as through the usage of `import { parseMarkdown } from \u0027@nuxtjs/mdc/runtime\u0027;`) will trigger the alert() dialog:\n\n```markdown\n# \u2705 This is correctly escaped by the parser\n\n- XSS Attempt:\n\n\u003ca href=\"javascript:alert(1)\"\u003e this gets sanitizied, yay!\u003c/a\u003e\n\n# \u274c These are vulnerable and not escaped\n\n- Bypass 1:\n\n\u003ca href=\"jav\u0026#x09;ascript:alert(\u0027XSS\u0027);\"\u003eClick Me 1\u003c/a\u003e\n\n- Bypass 2:\n\n\u003ca href=\"jav\u0026#x0A;ascript:alert(\u0027XSS\u0027);\"\u003eClick Me 2\u003c/a\u003e\n\n- Bypass 3:\n\n\u003ca href=\"jav\u0026#10;ascript:alert(\u0027XSS\u0027);\"\u003eClick Me 3\u003c/a\u003e\n```\n\n### Impact\n\nUsers who consume this library and perform markdown parsing from unvalidated sources such as LLM generative text responses, user input and other untrusted sources could result in rendering vulnerable XSS anchor links.\n\n## Reference\n\nYou may infer the following write-up for more in-depth walkthrough of URL parsing problems and suggestions on how to securely address them: [How to Parse URLs from Markdown to HTML Securely?](https://www.nodejs-security.com/blog/how-to-parse-urls-from-markdown-to-html-securely)",
"id": "GHSA-j82m-pc2v-2484",
"modified": "2025-02-13T16:49:46Z",
"published": "2025-02-06T17:16:27Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/nuxt-modules/mdc/security/advisories/GHSA-j82m-pc2v-2484"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-24981"
},
{
"type": "WEB",
"url": "https://github.com/nuxt-modules/mdc/commit/99097738b5561639e9bf247c55d8103236618bf3"
},
{
"type": "PACKAGE",
"url": "https://github.com/nuxt-modules/mdc"
},
{
"type": "WEB",
"url": "https://github.com/nuxt-modules/mdc/blob/main/src/runtime/parser/utils/props.ts#L16"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:L",
"type": "CVSS_V3"
}
],
"summary": "Parsed HTML anchor links in Markdown provided to parseMarkdown can result in XSS in @nuxtjs/mdc"
}
Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.