CVE-2026-27017
MEDIUMDescription
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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Exploit Intelligence
Low risk: more likely to be exploited than 5% of all known CVEs.
References
Related Vulnerabilities
Other CWE-1240 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2026-29146 | High | 7.5 | 6.3% | - | Fix |
| CVE-2025-29808 | Medium | 5.5 | 0.5% | - | Fix |
| CVE-2024-0220 | High | 8.3 | 0.4% | - | Fix |
| CVE-2025-24802 | High | 8.6 | 0.3% | - | - |
| CVE-2025-62514 | High | 8.3 | 0.3% | - | Fix |
| CVE-2025-53960 | Medium | 5.9 | 0.3% | - | Fix |
Common questions
How do I fix CVE-2026-27017?
Upgrade utls to 1.8.1 or later.
Is CVE-2026-27017 being actively exploited?
Not that we know of. CVE-2026-27017 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.15% is the estimated probability that it will be exploited in the next 30 days. That is higher than 5% of all scored CVEs.
How severe is CVE-2026-27017?
CVE-2026-27017 has a CVSS v3 base score of 5.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-27017 affect?
Published advisories record a fix for utls (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
Embed a live status badge for CVE-2026-27017
Markdown
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-02-20.