LeafKit's HTML escaping may be skipped for Collection values, enabling XSS
Priority HIGH 70CWE-116Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- Cross-site scripting
- Confidentiality · integrity · availability
- None · None · None
- Fix status
- Fixed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub. Impact type from CWE-79.
Summary
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.
Why it matters now
Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00281 20th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed leaf-kit (vapor): 1.14.2github.com/vapor/leaf-kit (SwiftURL): 1.14.2
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| vapor | leaf-kit | before 1.14.2 | 1.14.2 | Patch available | CNA |
| — | github.com/vapor/leaf-kit (SwiftURL) | before 1.14.2 | 1.14.2 | Patch available | GHSA-6jj5-j4j8-8473 |
- leaf-kit Vendorvapor Affected before 1.14.2 Fixed in 1.14.2 Patch available CNA
- github.com/vapor/leaf-kit (SwiftURL) Vendor— Affected before 1.14.2 Fixed in 1.14.2 Patch available GHSA-6jj5-j4j8-8473
Remediation
- Fix · CNA leaf-kit (vapor) Fixed in 1.14.2
- Fix · GHSA-6jj5-j4j8-8473 github.com/vapor/leaf-kit (SwiftURL) Fixed in 1.14.2 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2026-28499
- 2026-10-03 Alias added: GHSA-6jj5-j4j8-8473
References
More vapor Leafkit vulnerabilities
- TI-2026-21572 Leaf-kit html escaping does not work on characters that are part of extended grapheme cluster CVSS 3.1MEDIUM 6.1
- TI-2021-15509 LeafKit allows XSS with untrusted user input CVSS 3.1HIGH 7.4
Sources
- CVE-2026-28499 · CVE Program
- CVE-2026-28499 · NVD
- FIRST EPSS
- GHSA-6jj5-j4j8-8473 · GitHub Advisory Database · CC BY 4.0
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