CVE-2026-27120: Leafkit is a templating language with Swift-inspired syntax

Q: How do I fix CVE-2026-27120?

leafkit: upgrade to 1.14.1. Exact commands for each OS are on this page.

Q: Is CVE-2026-27120 being exploited?

CVE-2026-27120 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-2026-27120 affect?

CVE-2026-27120 affects leafkit. Severity is medium (CVSS 6.1). Leafkit is a templating language with Swift-inspired syntax. Prior to 1.4.1, htmlEscaped in leaf-kit will only escape html special characters if the extended grapheme clusters match, which allows bypassing escaping by using an extended grap

Q: How urgent is CVE-2026-27120?

Priority 31/100. Public exploit reference

Routine

MEDIUM 6.1UPGRADE

CVE-2026-27120 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 1.4.1, htmlEscaped in leaf-kit will only escape html special characters if the extended grapheme clusters match, which allows bypassing escaping by using an extended grapheme cluster containing both the special html character and some additional characters. In the case of html attributes, this can lead to XSS if there is a leaf variable in the attribute that is user controlled.

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 82%)
CISA exploited list	No
Weakness	CWE-75, CWE-79, CWE-87
Published	2026-02-20
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

2026-02-20 22:16 UTCPublished CVE record published
2026-06-17 10:26 UTCUpdated Record last modified

vapor leafkit UPGRADE

Affected: < 1.14.1

Fixed in: 1.14.1

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 1.14.1 (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-2026-27120?

leafkit: upgrade to 1.14.1. Exact commands for each OS are on this page.

Is CVE-2026-27120 being exploited?

CVE-2026-27120 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-2026-27120 affect?

CVE-2026-27120 affects leafkit. Severity is medium (CVSS 6.1). Leafkit is a templating language with Swift-inspired syntax. Prior to 1.4.1, htmlEscaped in leaf-kit will only escape html special characters if the extended grapheme clusters match, which allows bypassing escaping by using an extended grap

How urgent is CVE-2026-27120?

Priority 31/100. Public exploit reference

Software pages

Swift vulnerabilities

Related CVEs

CVE-2026-28499 MEDIUM 6.1 UPGRADE LeafKit is a templating language with Swift-inspired syntax

References

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