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Vulnerability · Published Feb 20, 2026 · Assigned by GitHub_M

CVE-2026-27017uTLS has a Chrome Parrot Fingerprint Vulnerability due to GREASE ECH Cipher Suite Mismatch

Low 2.3

In plain English

A low-severity security flaw in utls from refraction-networking. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 7% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)2.3Low
Exploit odds (30 days)0.2%top 92.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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 suite, it also uses AES for ECH. However, the Chrome parrot in uTLS hardcodes AES preference for outer cipher suites but selects the ECH cipher suite randomly between AES and ChaCha20. This creates a 50% chance of selecting ChaCha20 for ECH while using AES for the outer cipher suite, a combination impossible in Chrome. This issue only affects GREASE ECH; in real ECH, Chrome selects the first valid cipher suite when AES is preferred, which uTLS handles correctly. This issue has been fixed in version 1.8.1.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Gogithub.com/refraction-networking/utls1.8.1GHSA-7m29-f4hw-g2vx
Gogithub.com/refraction-networking/utls1.8.1GO-2026-4509
Ubuntu:22.04:LTSgolang-refraction-networking-utlsno fix listedUBUNTU-CVE-2026-27017
Ubuntu:24.04:LTSgolang-refraction-networking-utlsno fix listedUBUNTU-CVE-2026-27017
Ubuntu:25.10golang-refraction-networking-utlsno fix listedUBUNTU-CVE-2026-27017
Ubuntu:26.04:LTSgolang-refraction-networking-utlsno fix listedUBUNTU-CVE-2026-27017
Ubuntu:26.10golang-refraction-networking-utlsno fix listedUBUNTU-CVE-2026-27017

Affected products (as reported)

VendorProductVersions
refraction-networking utls >= 1.6.0, < 1.8.1

Weakness: CWE-1240 · Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

References