Vulnerability-Lookup

GHSA-7M29-F4HW-G2VX

Vulnerability from github – Published: 2026-02-18 22:33 – Updated: 2026-02-27 20:37

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.

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.

Severity ?

2.3 (Low)


                  
                    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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/refraction-networking/utls"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.6.0"
            },
            {
              "fixed": "1.8.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-27017"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1240"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-02-18T22:33:18Z",
    "nvd_published_at": "2026-02-20T03:16:01Z",
    "severity": "LOW"
  },
  "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.",
  "id": "GHSA-7m29-f4hw-g2vx",
  "modified": "2026-02-27T20:37:32Z",
  "published": "2026-02-18T22:33:18Z",
  "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "uTLS has a fingerprint vulnerability from GREASE ECH mismatch for Chrome parrots"
}

CVE-2026-27017 (GCVE-0-2026-27017)

Vulnerability from cvelistv5 – Published: 2026-02-20 02:47 – Updated: 2026-02-20 15:20

Title

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

Summary

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.

Severity ?

2.3 (Low)


                        
                          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

CWE

CWE-1240 - Use of a Cryptographic Primitive with a Risky Implementation

Assigner

GitHub_M

References

URL

Tags

https://github.com/refraction-networking/utls/sec…

x_refsource_CONFIRM

Impacted products

	Vendor	Product	Version
	refraction-networking	utls	Affected: >= 1.6.0, < 1.8.1

Show details on NVD website

JSON

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{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-27017",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-02-20T15:20:06.758492Z",
                "version": "2.0.3"
              },
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        "providerMetadata": {
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          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
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      }
    ],
    "cna": {
      "affected": [
        {
          "product": "utls",
          "vendor": "refraction-networking",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 1.6.0, \u003c 1.8.1"
            }
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        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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\u2014for 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."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "HIGH",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 2.3,
            "baseSeverity": "LOW",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "PASSIVE",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "LOW",
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      "problemTypes": [
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          "descriptions": [
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              "lang": "en",
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      "providerMetadata": {
        "dateUpdated": "2026-02-20T02:47:17.899Z",
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      "references": [
        {
          "name": "https://github.com/refraction-networking/utls/security/advisories/GHSA-7m29-f4hw-g2vx",
          "tags": [
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      "source": {
        "advisory": "GHSA-7m29-f4hw-g2vx",
        "discovery": "UNKNOWN"
      },
      "title": "uTLS has a Chrome Parrot Fingerprint Vulnerability due to GREASE ECH Cipher Suite Mismatch"
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  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
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    "datePublished": "2026-02-20T02:47:17.899Z",
    "dateReserved": "2026-02-17T03:08:23.490Z",
    "dateUpdated": "2026-02-20T15:20:18.976Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-7M29-F4HW-G2VX

CVE-2026-27017 (GCVE-0-2026-27017)

Tags

Sightings

Nomenclature