CVE-2026-27017

LOW EPSS 4.9%
Published Feb 20, 20264mo ago · Modified Jun 17, 20262w ago
2.3 CVSS 4.0
Low
Find Similar
Published Feb 20, 2026 4mo ago
Last Modified Jun 17, 2026 2w ago

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.

CVSS Details

Base Score
2.3
Exploitability
—
Impact
—
Vector string
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
Attack Vector Network
Attack Complexity High
Privileges Required None
User Interaction P
Scope X

Threat Intelligence

EPSS Exploit Probability
4.9% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 1

CWE-1240

Affected Products 1

VendorProductVersionRange
refraction-networkingutls*≥1.6.0  –  <1.8.1

References 1

  • github.com https://github.com/refraction-networking/utls/security/advisories/GHSA-7m29-f4hw-g2vx
    PatchVendor Advisory

Remediation

  • github.com https://github.com/refraction-networking/utls/security/advisories/GHSA-7m29-f4hw-g2vx
    PatchVendor Advisory