CVE-2026-27120— Leaf-kit html escaping does not work on characters that are part of extended grapheme cluster
Quick assessment
Affected
vapor leaf-kit
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
leafkit是Vapor开源的一个应用软件。使用 Swift 创建模块化服务器端软件。 leafkit 1.4.1之前版本存在安全漏洞，该漏洞源于htmlEscaped仅匹配扩展字素簇，可能导致绕过转义和跨站脚本攻击。
Possible ATT&CK Techniques 1 AI
T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-27120
Vulnerability Information
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Vulnerability Title
Leaf-kit html escaping does not work on characters that are part of extended grapheme cluster
Source: CVE Program / CVE List V5
Vulnerability Description
Leafkit is a templating language with Swift-inspired syntax. Prior to 1.4.1, htmlEscaped in leaf-kit will only escape html special characters if the extended grapheme clusters match, which allows bypassing escaping by using an extended grapheme cluster containing both the special html character and some additional characters. In the case of html attributes, this can lead to XSS if there is a leaf variable in the attribute that is user controlled. This vulnerability is fixed in 1.4.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
特殊命令到另一不同平面时的净化处理不恰当(特殊命令注入)
Source: CVE Program / CVE List V5
Vulnerability Title
leafkit 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
leafkit是Vapor开源的一个应用软件。使用 Swift 创建模块化服务器端软件。 leafkit 1.4.1之前版本存在安全漏洞，该漏洞源于htmlEscaped仅匹配扩展字素簇，可能导致绕过转义和跨站脚本攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
II. Public POCs for CVE-2026-27120
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V. Comments for CVE-2026-27120
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