Summary
There is a fingerprint mismatch with Chrome when using GREASE ECH, having to do with ciphersuite selection. When Chrome selects the preferred ciphersuite in the outer ClientHello and the ciphersuite for ECH, it does so consistently based on hardware support. That means, for example, if it prefers AES for the outer ciphersuite, it would also use AES for ECH. The Chrome parrot in utls hardcodes AES preference for outer ciphersuites but selects the ECH ciphersuite randomly between AES and ChaCha20. So there is a 50% chance of selecting ChaCha20 for ECH while using AES for the outer ciphersuite, which is impossible in Chrome.
This is only a problem in GREASE ECH, since in real ECH Chrome selects the first valid ciphersuite when AES is preferred, which is the same in utls. So no change is done there.
Affected symbols: HelloChrome_120, HelloChrome_120_PQ, HelloChrome_131, HelloChrome_133
Fix commit: 24bd1e05a788c1add7f3037f4532ea552b2cee07
Thanks to telegram @acgdaily for reporting this issue.
Impact
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-27017? CVE-2026-27017 is a low-severity security vulnerability in github.com/refraction-networking/utls (go), affecting versions >= 1.6.0, < 1.8.1. It is fixed in 1.8.1.
- Which versions of github.com/refraction-networking/utls are affected by CVE-2026-27017? github.com/refraction-networking/utls (go) versions >= 1.6.0, < 1.8.1 is affected.
- Is there a fix for CVE-2026-27017? Yes. CVE-2026-27017 is fixed in 1.8.1. Upgrade to this version or later.
- Is CVE-2026-27017 exploitable, and should I be worried? Whether CVE-2026-27017 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-27017 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-27017? Upgrade
github.com/refraction-networking/utlsto 1.8.1 or later.