CVE-2026-27017

Aliases:GHSA-7m29-f4hw-g2vxGO-2026-4509CGA-78cc-745h-7q2jCGA-m5gj-jx2w-f89v
Advisory lineage Upstream: 0 Downstream: 5
Analyzed
Published: 20 Feb 2026, 02:47
Last modified:20 Feb 2026, 15:20

Vulnerability Summary

Overall Risk (default)
low
21/100
CVSS Score
5.3 MEDIUM
v3.1 (nvd)
EPSS Score
0.16% LOW
0% probability +0.15%
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

20 Feb 2026, 02:47
Published
Vulnerability first disclosed
20 Feb 2026, 15:20
Last Modified
Vulnerability information updated

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 Metrics

  • v4.0•LOW•Score: 2.3CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
  • v4.0•LOW•Score: 2.3CVSS: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
  • v3.1•MEDIUM•Score: 5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS Trends

Current EPSS score: 0.16%• Percentile: 6%

Techniques & Countermeasures

  • 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.

Affected Systems

  • chainguard•nuclei

    < 3.7.0-r4

  • wolfi•nuclei

    < 3.7.0-r4

  • github.com/refraction-networking•utls

    ≥ 1.6.0, < 1.8.1

  • refraction-networking•utls

    ≥ 1.6.0, < 1.8.1

References (7)