Moderate severityNVD Advisory· Published Feb 20, 2026· Updated Feb 24, 2026
Leaf-kit html escaping does not work on characters that are part of extended grapheme cluster
CVE-2026-27120
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.
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Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
github.com/vapor/leaf-kitSwiftURL | < 1.4.1 | 1.4.1 |
Affected products
2- vapor/leaf-kitv5Range: < 1.4.1
Patches
Vulnerability mechanics
References
4- github.com/advisories/GHSA-4hfh-fch3-5q7pghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-27120ghsaADVISORY
- github.com/vapor/leaf-kit/commit/8919e39476c3a4ba05c28b71546bb9195f87ef34ghsax_refsource_MISCWEB
- github.com/vapor/leaf-kit/security/advisories/GHSA-4hfh-fch3-5q7pghsax_refsource_CONFIRMWEB
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