VYPR
High severity7.4NVD Advisory· Published Aug 9, 2021· Updated Jun 17, 2026

CVE-2021-37634

CVE-2021-37634

Description

Leafkit is a templating language with Swift-inspired syntax. Versions prior to 1.3.0 are susceptible to Cross-site Scripting (XSS) attacks. This affects anyone passing unsanitised data to Leaf's variable tags. Before this fix, Leaf would not escape any strings passed to tags as variables. If an attacker managed to find a variable that was rendered with their unsanitised data, they could inject scripts into a generated Leaf page, which could enable XSS attacks if other mitigations such as a Content Security Policy were not enabled. This has been patched in 1.3.0. As a workaround sanitize any untrusted input before passing it to Leaf and enable a CSP to block inline script and CSS data.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
github.com/vapor/leaf-kitSwiftURL
< 1.3.01.3.0

Affected products

3

Patches

Vulnerability mechanics

References

5

News mentions

0

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