CVE-2026-27120Public exploitNetwork attack vector

Cross-site scripting via grapheme-cluster escape bypass

Published Feb 20, 2026 · Updated Feb 20, 2026

Cross-site scripting in Vapor LeafKit before 1.4.1 allows remote attackers to inject JavaScript through user-controlled HTML attributes. The htmlEscaped function applies Swift grapheme-cluster replacement, so an HTML metacharacter joined to a combining character is not encoded. Exploitation requires an application to place attacker-controlled data in an attribute and a user to render it without an effective CSP, enabling script execution in that user's browser.

CVSS severity6.1
Medium
EPSS probability0.23%
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 Vapor LeafKit before 1.4.1 allows remote attackers to inject JavaScript through user-controlled HTML attributes. The htmlEscaped function applies Swift grapheme-cluster replacement, so an HTML metacharacter joined to a combining character is not encoded. Exploitation requires an application to place attacker-controlled data in an attribute and a user to render it without an effective CSP, enabling script execution in that user's browser.

The record

CVE
CVE-2026-27120
Published
Feb 20, 2026
Updated
Feb 20, 2026
Vendor
Vapor
Product
LeafKit
Classifications
CWE-79, CWE-87, CWE-75, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.4.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Vapor · LeafKitversion=< 1.4.1

Published CVSS scores

6.1GitHubCVSS: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')
CWE-87Improper Neutralization of Alternate XSS Syntax
CWE-75Failure to Sanitize Special Elements into a Different Plane (Special Element Injection)
T1203Exploitation for Client Execution

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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