CVE-2026-27120

MEDIUM6.1

Leaf-kit html escaping does not work on characters that are part of extended grapheme cluster

Published Feb 20, 2026

Modified 1 weeks ago

Details

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.

References

WEB

https://github.com/vapor/leaf-kit/commit/8919e39476c3a4ba05c28b71546bb9195f87ef34

WEB

https://github.com/vapor/leaf-kit/security/advisories/GHSA-4hfh-fch3-5q7p

ADVISORY

https://www.cve.org/CVERecord?id=CVE-2026-27120

CVSS Analysis

CVSS v3.1

6.1

Exploitability

Attack Vector