vapor leaf-kit up to 1.4.0 Special Character cross site scripting

Summaryinfo

A vulnerability was found in vapor leaf-kit up to 1.4.0. It has been rated as problematic. Affected by this issue is some unknown functionality of the component Special Character Handler. The manipulation leads to cross site scripting. This vulnerability is traded as CVE-2026-27120. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in vapor leaf-kit up to 1.4.0. This issue affects an unknown function of the component Special Character Handler. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-27120 since 02/17/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

Upgrading to version 1.4.1 eliminates this vulnerability. Applying the patch 8919e39476c3a4ba05c28b71546bb9195f87ef34 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• vapor

Name

• leaf-kit

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4.0

License

• open-source

Website

• Product: https://github.com/vapor/leaf-kit/

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CPE 2.2info

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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