What is CVE-2026-28499?

CVE-2026-28499 is a medium-severity vulnerability in Vapor Leaf-Kit, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-03-18.

How severe is CVE-2026-28499?

Medium severity. CVSS v3 base score is 6.1 out of 10.

XSS in Vapor Leaf-Kit

CVE-2026-28499

LeafKit is a templating language with Swift-inspired syntax. Prior to version 1.14.2, HTML escaping doesn't work correctly when a template prints a collection (Array / Dictionary) via `#(value)`. This can result in XSS, allowing potentially untrusted input to be rendered unescaped. Version 1.14.2 fixes the issue.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2026-03-18 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.003 (24.3th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 24th percentile — 24.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.001

Affected products

Vapor Leaf-Kit — versions < 1.14.2
Vapor Leafkit

Weakness classification (CWE)

References

github.com/vapor/leaf-kit/security/advisories/GHSA-6jj5-j4j8-8473 (Exploit, Vendor Advisory)
github.com/vapor/leaf-kit/commit/6044b844caa858a0c5f2505ac166f5a057c990dc (Patch)
github.com/vapor/leaf-kit/releases/tag/1.14.2 (Release Notes)

Frequently asked questions

What is CVE-2026-28499?: CVE-2026-28499 is a medium-severity vulnerability in Vapor Leaf-Kit, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-03-18.
How severe is CVE-2026-28499?: Medium severity. CVSS v3 base score is 6.1 out of 10.