Vulnerability · Published Feb 20, 2026 · Assigned by GitHub_M

CVE-2026-27120Leaf-kit html escaping does not work on characters that are part of extended grapheme cluster

Medium 6.1

In plain English

A medium-severity cross-site scripting in leaf-kit from vapor. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 19% of all known vulnerabilities).

Severity (CVSS 3.1)6.1Medium

Exploit odds (30 days)0.3%top 81.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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.

Affected products (as reported)

Vendor	Product	Versions
vapor	leaf-kit	< 1.4.1

Weakness: CWE-75, CWE-79, CWE-87 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

References

https://github.com/vapor/leaf-kit/security/advisories/GHSA-4hfh-fch3-5q7p x_refsource_CONFIRM
https://github.com/vapor/leaf-kit/commit/8919e39476c3a4ba05c28b71546bb9195f87ef34 x_refsource_MISC