{"id":"CVE-2021-37634","aliases":["GHSA-rv3x-xq3r-8j9h"],"url":"https://o3.security/vulnerability/CVE-2021-37634","summary":"LeafKit allows XSS with untrusted user input","details":"### Impact\nThis 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.\n\n### Patches\nThis has been patched in 1.3.0\n\n### Workarounds\nSanitise any untrusted input before passing it to Leaf and enable a CSP to block inline script and CSS data.\n\n### References\nhttps://github.com/vapor/leaf-kit-ghsa-rv3x-xq3r-8j9h/pull/1\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [Leaf Kit](https://github.com/vapor/leaf-kit)\n* Email us at [security@vapor.codes](mailto:security@vapor.codes)","published":"2021-08-09T20:15:07.727Z","modified":"2026-10-20T10:54:50.053357717Z","cvss":{"score":6.1,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"},"epss":{"score":0.0071,"percentile":0.51914,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"SwiftURL","name":"github.com/vapor/leaf-kit","fixedVersion":"1.3.0"}],"fix":{"url":"https://github.com/vapor/leaf-kit-ghsa-rv3x-xq3r-8j9h/pull/1","label":"vapor/leaf-kit-ghsa-rv3x-xq3r-8j9h#1"},"references":[{"type":"ADVISORY","url":"https://github.com/vapor/leaf-kit/security/advisories/GHSA-rv3x-xq3r-8j9h"},{"type":"FIX","url":"https://github.com/vapor/leaf-kit-ghsa-rv3x-xq3r-8j9h/pull/1"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-37634"},{"type":"PACKAGE","url":"https://github.com/vapor/leaf-kit"},{"type":"WEB","url":"https://github.com/vapor/leaf-kit/releases/tag/1.3.0"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-20T10:54:50.053357717Z"}}