CVE-2026-31873
ADVISORY - githubSummary
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
}
Common Weakness Enumeration (CWE)
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
GitHub
3.9
CVSS SCORE
N/Aunspecified| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| unhead | npm | - | - | <=2.1.10 | 2.1.11 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.
The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
The vulnerable system can be exploited without interaction from any user.
An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
There is no loss of confidentiality.
There is no loss of trust or accuracy within the impacted component.
There is no impact to availability within the impacted component.