CVE-2026-27017: Github.com/refraction networking/utls UTLS Has A Fingerprint Vulnerability Vulnerability

LOW
Advisory Identifier: GHSA-7m29-f4hw-g2vx
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CWE-1240
Published
Advisory Summary

CVE-2026-27017 is a LOW utls has a fingerprint vulnerability vulnerability (CWE-1240: Use of a Cryptographic Primitive with a Risky Implementation) affecting Github.com/refraction networking/utls libraries in the Go ecosystem. The issue involves utls has a fingerprint vulnerability from grease ech mismatch for chrome parrots. Remediation is available by upgrading affected packages to version 1.8.1.

CVE-2026-27017 at a Glance

CVE Identifier CVE-2026-27017
GHSA Identifier GHSA-7m29-f4hw-g2vx
Severity LOW
CVSS v3.1 Base Score N/A
CWE Classification CWE-1240: Use of a Cryptographic Primitive with a Risky Implementation
Affected Product Github.com/refraction networking/utls
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2026-27017

To remediate this vulnerability, upgrade all affected Github.com/refraction networking/utls dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/refraction-networking/utls fixed: 1.8.1 
Upgrade github.com/refraction-networking/utls to 1.8.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/refraction-networking/utls

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-27017, inspect your project dependencies for Github.com/refraction networking/utls:

inspect dependencies for github.com/refraction-networking/utls

Analyze the terminal output to locate any version of Github.com/refraction networking/utls in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.8.1), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1240: Use of a Cryptographic Primitive with a Risky Implementation, where to fulfill the need for a cryptographic primitive, the product implements a cryptographic algorithm using a non-standard, unproven, or disallowed/non-compliant cryptographic implementation. In Github.com/refraction networking/utls, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2026-27017 Affected Github.com/refraction networking/utls Versions

1 component(s)
Fixed Versions:
1.8.1
Product / Package Ecosystem Affected Versions Fixed Version
github.com/refraction-networking/utls
golang/github.com/refraction-networking/utls
Go
≥ 1.6.0
< 1.8.1
1.8.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/refraction-networking/utls/security/advisories/GHSA-7m29-f4hw-g2vx
NVD — CVE-2026-27017 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27017
Security Fix Commit FIX COMMIT
https://github.com/refraction-networking/utls/commit/24bd1e05a788c1add7f3037f4532ea552b2cee07
Github.com/refraction networking/utls Source Repository REPOSITORY
https://github.com/refraction-networking/utls
Github.com/refraction networking/utls Release RELEASE
https://github.com/refraction-networking/utls/releases/tag/v1.8.1
pkg.go.dev/vuln/go-2026-4509 WEB
https://pkg.go.dev/vuln/GO-2026-4509

Frequently Asked Questions

What is CVE-2026-27017?
CVE-2026-27017 is a security vulnerability in Github.com/refraction networking/utls involving uTLS has a fingerprint vulnerability from GREASE ECH mismatch for Chrome parrots under CWE-1240: Use of a Cryptographic Primitive with a Risky Implementation.
Which Github.com/refraction networking/utls versions are affected?
Affected versions include releases prior to 1.8.1 across affected packages: github.com/refraction-networking/utls.
What version fixes CVE-2026-27017?
Upgrading to 1.8.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/refraction-networking/utls affected?
Yes, github.com/refraction-networking/utls is affected in releases prior to 1.8.1. Upgrade your dependency to 1.8.1 or later.
What CWE is associated with CVE-2026-27017?
CVE-2026-27017 is classified under CWE-1240: Use of a Cryptographic Primitive with a Risky Implementation (To fulfill the need for a cryptographic primitive, the product implements a cryptographic algorithm using a non-standard, unproven, or disallowed/non-compliant cryptographic implementation.).
How can I check Go dependencies for CVE-2026-27017?
Run the dependency tree command: 'inspect dependencies for github.com/refraction-networking/utls'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7m29-f4hw-g2vx",
  "modified" : "2026-02-27T20:37:32Z",
  "published" : "2026-02-18T22:33:18Z",
  "aliases" : [ "CVE-2026-27017" ],
  "summary" : "uTLS has a fingerprint vulnerability from GREASE ECH mismatch for Chrome parrots",
  "details" : "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.\n\nThis 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.\n\nAffected symbols: `HelloChrome_120`, `HelloChrome_120_PQ`, `HelloChrome_131`, `HelloChrome_133`\n\nFix commit: 24bd1e05a788c1add7f3037f4532ea552b2cee07\n\nThanks to telegram @acgdaily for reporting this issue.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/refraction-networking/utls"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.6.0"
      }, {
        "fixed" : "1.8.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/refraction-networking/utls/security/advisories/GHSA-7m29-f4hw-g2vx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27017"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/refraction-networking/utls/commit/24bd1e05a788c1add7f3037f4532ea552b2cee07"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/refraction-networking/utls"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/refraction-networking/utls/releases/tag/v1.8.1"
  }, {
    "type" : "WEB",
    "url" : "https://pkg.go.dev/vuln/GO-2026-4509"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1240" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-18T22:33:18Z",
    "nvd_published_at" : "2026-02-20T03:16:01Z"
  }
}