CVE-2026-28499: LeafKit is a templating language with Swift-inspired syntax

Q: How do I fix CVE-2026-28499?

leafkit: upgrade to 1.14.2. Exact commands for each OS are on this page.

Q: Is CVE-2026-28499 being exploited?

CVE-2026-28499 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-28499 affect?

CVE-2026-28499 affects leafkit. Severity is medium (CVSS 6.1). 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

Q: How urgent is CVE-2026-28499?

Priority 31/100. Public exploit reference

Routine

MEDIUM 6.1UPGRADE

CVE-2026-28499 is a medium-severity flaw (CVSS 6.1) affecting leafkit. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 80%)
CISA exploited list	No
Weakness	CWE-79, CWE-80, CWE-116
Published	2026-03-18
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: vapor

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-18 02:16 UTCPublished CVE record published
2026-06-17 10:28 UTCUpdated Record last modified

vapor leafkit UPGRADE

Affected: < 1.14.2

Fixed in: 1.14.2

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy leafkit || rpm -q leafkit || leafkit --version

2. UPGRADE to 1.14.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade leafkit

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade leafkit

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-28499?

leafkit: upgrade to 1.14.2. Exact commands for each OS are on this page.

Is CVE-2026-28499 being exploited?

CVE-2026-28499 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-28499 affect?

CVE-2026-28499 affects leafkit. Severity is medium (CVSS 6.1). 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

How urgent is CVE-2026-28499?

Priority 31/100. Public exploit reference

Software pages

Swift vulnerabilities

Related CVEs

CVE-2026-27120 MEDIUM 6.1 UPGRADE Leafkit is a templating language with Swift-inspired syntax

References

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