GHSA-7m29-f4hw-g2vxPublished

uTLS has a Chrome Parrot Fingerprint Vulnerability due to GREASE ECH Cipher Suite Mismatch

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cve-program · CVE-2026-27017

Published

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.

Source published: 20 Feb 2026 02:47:17 UTC
Source modified: 20 Feb 2026 15:20:18 UTC
Saved here: 23 Oct 2026 15:48:27 UTC
Source terms: CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 4.0 · 2.3 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

euvd · EUVD-2026-8031

Published

Additional publisher context

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

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datePublished: Feb 20, 2026, 2:47:17 AM

dateUpdated: Feb 20, 2026, 3:20:18 PM

2 related source bulletins · separate from aliases

openSUSE-SU-2026:21653-1: Security update for v2ray-core

CVE-2026-27017 · CVE-2026-39821 · CVE-2026-72815 · CVE-2026-72816 · CVE-2026-72817

openSUSE-SU-2026:10913-1: golang-github-v2fly-v2ray-core-5.51.2-1.1 on GA media

CVE-2026-27017 · CVE-2026-39821

Source published: Feb 20, 2026, 2:47:17 AM (timezone not stated)
Source modified: Feb 20, 2026, 3:20:18 PM (timezone not stated)
Saved here: 15 Nov 2026 08:36:03 UTC
Source terms: ENISA EUVD · source terms and attribution apply

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EUVD CVSS 4.0 · 2.3 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

nvd · CVE-2026-27017

Published

Additional publisher context

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Analyzed

Weakness classifications: CWE-1240

Original publisher date fields

published: 2026-02-20T03:16:01.797

lastModified: 2026-06-17T10:26:32.577

1 source CPE criteria · context only

cpe:2.3:a:refraction-networking:utls:*:*:*:*:*:go:*:*

The original JSON retains the logical configuration operators, exclusions and version bounds.

Source published: 20 Feb 2026 03:16:01 UTC
Source modified: 17 Jun 2026 10:26:32 UTC
Saved here: 25 Oct 2026 06:17:28 UTC
Source terms: NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 4.0 · [email protected] · Secondary · 2.3 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Primary · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

osv · GHSA-7m29-f4hw-g2vx

Published

There is a fingerprint mismatch with Chrome when using GREASE ECH, having to do with ciphersuite selection. When Chrome selects the preferred ciphersuite in the outer ClientHello and the ciphersuite for ECH, it does so consistently based on hardware support. That means, for example, if it prefers AES for the outer ciphersuite, it would also use AES for ECH. The Chrome parrot in utls hardcodes AES preference for outer ciphersuites but selects the ECH ciphersuite randomly between AES and ChaCha20. So there is a 50% chance of selecting ChaCha20 for ECH while using AES for the outer ciphersuite, which is impossible in Chrome. This is only a problem in GREASE ECH, since in real ECH Chrome selects the first valid ciphersuite when AES is preferred, which is the same in utls. So no change is done there. Affected symbols: `HelloChrome_120`, `HelloChrome_120_PQ`, `HelloChrome_131`, `HelloChrome_133` Fix commit: 24bd1e05a788c1add7f3037f4532ea552b2cee07 Thanks to telegram @acgdaily for reporting this issue.

Source published: 18 Feb 2026 22:33:18 UTC
Source modified: 10 Sep 2026 03:50:34 UTC
Saved here: 24 Oct 2026 13:19:41 UTC
Source terms: GitHub Advisory Database · CC-BY-4.0

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Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V4 · 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

Publisher rating · LOW

osv · GO-2026-4509

Published

Fingerprint vulnerability in uTLS from GREASE ECH mismatch for Chrome parrots in github.com/refraction-networking/utls

Source published: 24 Feb 2026 23:10:26 UTC
Source modified: 24 Feb 2026 23:41:14 UTC
Saved here: 24 Oct 2026 13:19:41 UTC
Source terms: OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · OSV · upstream source license applies. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.