CVE-2026-27017Network attack vector

Client fingerprint disclosure via inconsistent GREASE ECH ciphers

Published Feb 20, 2026 · Updated Feb 20, 2026

Fingerprint disclosure in Refraction Networking uTLS 1.6.0 through 1.8.0 allows remote attackers to identify Chrome-parrot clients via GREASE ECH. BoringGREASEECH offers both AES-GCM and ChaCha20 while the outer Chrome-parrot ClientHello always prefers AES, producing an impossible Chrome combination half the time. Exposure requires an affected Chrome ClientHello symbol and GREASE ECH; real ECH is unaffected, and the consequence is limited to loss of fingerprint resistance.

CVSS severity2.3
Low
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Fingerprint disclosure in Refraction Networking uTLS 1.6.0 through 1.8.0 allows remote attackers to identify Chrome-parrot clients via GREASE ECH. BoringGREASEECH offers both AES-GCM and ChaCha20 while the outer Chrome-parrot ClientHello always prefers AES, producing an impossible Chrome combination half the time. Exposure requires an affected Chrome ClientHello symbol and GREASE ECH; real ECH is unaffected, and the consequence is limited to loss of fingerprint resistance.

The record

CVE
CVE-2026-27017
Published
Feb 20, 2026
Updated
Feb 20, 2026
Vendor
Refraction Networking
Product
uTLS
Classifications
CWE-1240
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 1.6.0, < 1.8.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Refraction Networking · uTLSversion=>= 1.6.0, < 1.8.1

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
2.3GitHub, Inc.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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

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

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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