CVE-2026-27017: uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprinting resistance while still using

Routine

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-27017 is a medium-severity flaw (CVSS 5.3) affecting utls. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprinting resistance while still using it for the handshake. Versions 1.6.0 through 1.8.0 contain a fingerprint mismatch with Chrome when using GREASE ECH, related to cipher suite selection. When Chrome selects the preferred cipher suite in the outer ClientHello and for ECH, it does so consistently based on hardware support—for example, if it prefers AES for the outer cipher

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 93%)
CISA exploited list	No
Weakness	CWE-1240
Published	2026-02-20
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: refraction-networking

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 03:16 UTCPublished CVE record published
2026-06-17 10:26 UTCUpdated Record last modified

refraction-networking utls UPGRADE

Affected: >= 1.6.0 and < 1.8.1

Fixed in: 1.8.1

Safe to downgrade to: a release before 1.6.0

1. Check installed version

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

2. UPGRADE to 1.8.1 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade utls

Note

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

3. If no update is available yet, DOWNGRADE to a release before 1.6.0 (Debian / Ubuntu)

apt-cache madison utls sudo apt install utls=<VERSION_BEFORE_1.6.0> sudo apt-mark hold utls

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list utls sudo dnf downgrade utls-<VERSION_BEFORE_1.6.0> sudo dnf versionlock add utls

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2026-27017?

utls: upgrade to 1.8.1. Exact commands for each OS are on this page.

Is CVE-2026-27017 being exploited?

CVE-2026-27017 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-2026-27017 affect?

CVE-2026-27017 affects utls. Severity is medium (CVSS 5.3). uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprinting resistance while still using it for the handshake. Versions 1.6.0 through 1.8.0 contain a fingerprint mismatch with Chrome when using GREASE ECH, related to c

How urgent is CVE-2026-27017?

Priority 25/100. Remotely exploitable, no login, no user action

Software pages

Google Chrome vulnerabilities

Related CVEs

CVE-2026-26994 MEDIUM 6.5 UPGRADE uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprinting resistance while still using

References

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