Cross-site scripting via unsanitized attribute names
Published Mar 12, 2026 · Updated Mar 12, 2026
Cross-site scripting in UnJS Unhead before 2.1.11 allows remote attackers to execute JavaScript through crafted SSR head attributes. The acceptDataAttrs function accepts any key beginning with data-, and propsToString inserts that key unescaped into serialized HTML, so spaces create event-handler attributes. Exploitation requires an application to pass attacker-controlled metadata to useHeadSafe and a visitor to render the affected page, exposing that visitor's browser context.
Summary
What happened
Cross-site scripting in UnJS Unhead before 2.1.11 allows remote attackers to execute JavaScript through crafted SSR head attributes. The acceptDataAttrs function accepts any key beginning with data-, and propsToString inserts that key unescaped into serialized HTML, so spaces create event-handler attributes. Exploitation requires an application to pass attacker-controlled metadata to useHeadSafe and a visitor to render the affected page, exposing that visitor's browser context.
The record
- CVE
- CVE-2026-31860
- Published
- Mar 12, 2026
- Updated
- Mar 12, 2026
- Vendor
- UnJS
- Product
- Unhead
- Classifications
- CWE-79, T1059.007
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 12, 2026CVE publishedPublication date reported by the CVE source.
- Mar 12, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 2.1.11
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Upstream useHeadSafe attribute-name injection proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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