Vulnerability 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 Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Refraction-Networking | Utls | >= 1.6.0, < 1.8.1 |
Related Weaknesses (CWE)
References
- https://github.com/refraction-networking/utls/security/advisories/GHSA-7m29-f4hwVendor AdvisoryPatch
FAQ
What is CVE-2026-27017?
CVE-2026-27017 is a vulnerability with a CVSS score of 5.3 (MEDIUM). 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 Ch...
How severe is CVE-2026-27017?
CVE-2026-27017 has been rated MEDIUM with a CVSS base score of 5.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-27017?
Check the references section above for vendor advisories and patch information. Affected products include: Refraction-Networking Utls.