GHSA-5339-HVWR-7582
Vulnerability from github – Published: 2026-03-12 14:19 – Updated: 2026-03-12 19:14
VLAI
Summary
Unhead Vulnerable to Bypass of URI Scheme Sanitization in makeTagSafe via Case-Sensitivity
Details
The link.href check in makeTagSafe (safe.ts, line 68-71) uses String.includes(), which is case-sensitive:
if (key === 'href') {
if (val.includes('javascript:') || val.includes('data:')) {
return
}
next[key] = val
}
Browsers treat URI schemes case-insensitively. DATA:text/css,... is the same as data:text/css,... to the browser, but 'DATA:...'.includes('data:') returns false.
PoC
useHeadSafe({
link: [{
rel: 'stylesheet',
href: 'DATA:text/css,body{display:none}'
}]
})
SSR output:
<link rel="stylesheet" href="DATA:text/css,body{display:none}">
The browser loads this as a CSS stylesheet. An attacker can inject arbitrary CSS for UI redressing or data exfiltration via CSS attribute selectors with background-image callbacks.
Any case variation works: DATA:, Data:, dAtA:, JAVASCRIPT:, etc.
Suggested fix
if (key === 'href') {
const lower = val.toLowerCase()
if (lower.includes('javascript:') || lower.includes('data:')) {
return
}
next[key] = val
}
Severity
0.0 (None)
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 2.1.10"
},
"package": {
"ecosystem": "npm",
"name": "unhead"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.1.11"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-31873"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": true,
"github_reviewed_at": "2026-03-12T14:19:25Z",
"nvd_published_at": "2026-03-12T18:16:24Z",
"severity": "LOW"
},
"details": "The `link.href` check in `makeTagSafe` (safe.ts, line 68-71) uses `String.includes()`, which is case-sensitive:\n\n```typescript\nif (key === \u0027href\u0027) {\n if (val.includes(\u0027javascript:\u0027) || val.includes(\u0027data:\u0027)) {\n return\n }\n next[key] = val\n}\n```\n\nBrowsers treat URI schemes case-insensitively. `DATA:text/css,...` is the same as `data:text/css,...` to the browser, but `\u0027DATA:...\u0027.includes(\u0027data:\u0027)` returns `false`.\n\n### PoC\n\n```javascript\nuseHeadSafe({\n link: [{\n rel: \u0027stylesheet\u0027,\n href: \u0027DATA:text/css,body{display:none}\u0027\n }]\n})\n```\n\nSSR output:\n\n```html\n\u003clink rel=\"stylesheet\" href=\"DATA:text/css,body{display:none}\"\u003e\n```\n\nThe browser loads this as a CSS stylesheet. An attacker can inject arbitrary CSS for UI redressing or data exfiltration via CSS attribute selectors with background-image callbacks.\n\nAny case variation works: `DATA:`, `Data:`, `dAtA:`, `JAVASCRIPT:`, etc.\n\n## Suggested fix\n\n```typescript\nif (key === \u0027href\u0027) {\n const lower = val.toLowerCase()\n if (lower.includes(\u0027javascript:\u0027) || lower.includes(\u0027data:\u0027)) {\n return\n }\n next[key] = val\n}\n```",
"id": "GHSA-5339-hvwr-7582",
"modified": "2026-03-12T19:14:29Z",
"published": "2026-03-12T14:19:25Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/unjs/unhead/security/advisories/GHSA-5339-hvwr-7582"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31873"
},
{
"type": "PACKAGE",
"url": "https://github.com/unjs/unhead"
},
{
"type": "WEB",
"url": "https://github.com/unjs/unhead/releases/tag/v2.1.11"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:N",
"type": "CVSS_V3"
}
],
"summary": "Unhead Vulnerable to Bypass of URI Scheme Sanitization in makeTagSafe via Case-Sensitivity"
}
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Sightings
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
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They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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