CVE-2026-31873Public exploitNetwork attack vector

CSS injection via case-sensitive URI scheme filtering

Published Mar 12, 2026 · Updated Mar 12, 2026

Cross-site scripting in UnJS Unhead before 2.1.11 allows remote attackers to inject arbitrary CSS through a crafted link href. makeTagSafe checks link.href for lowercase data: and javascript: substrings with case-sensitive String.includes(), then emits mixed-case schemes that browsers accept. Exploitation requires attacker-controlled input to reach useHeadSafe; rendered CSS enables UI redressing or data exfiltration through selector-triggered callbacks.

CVSS severity6.1
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in UnJS Unhead before 2.1.11 allows remote attackers to inject arbitrary CSS through a crafted link href. makeTagSafe checks link.href for lowercase data: and javascript: substrings with case-sensitive String.includes(), then emits mixed-case schemes that browsers accept. Exploitation requires attacker-controlled input to reach useHeadSafe; rendered CSS enables UI redressing or data exfiltration through selector-triggered callbacks.

The record

CVE
CVE-2026-31873
Published
Mar 12, 2026
Updated
Mar 12, 2026
Vendor
UnJS
Product
Unhead
Classifications
CWE-79
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 12, 2026CVE publishedPublication date reported by the CVE source.
  2. 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.

  1. Affected versionversion=< 2.1.11

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

UnJS · Unheadversion=< 2.1.11

Published CVSS scores

0.0GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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