GHSA-7m29-f4hw-g2vx: github.com/refraction-networking/utls (CVE-2026-27017)

Package	Ecosystem	Affected	Fixed in
github.com/refraction-networking/utls	Go	>=1.6.0, <1.8.1	1.8.1

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

The uTLS Go library, versions 1.6.0 up to but not including 1.8.1, has a fingerprint mismatch with Chrome when using GREASE ECH: the Chrome parrot can pick a ChaCha20 ciphersuite for ECH while using AES for the outer ciphersuite, which real Chrome never does. An attacker could use this to tell uTLS traffic apart from genuine Chrome traffic, and the advisory rates the severity as low. Upgrade to version 1.8.1 or later. The source gives no workaround.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
2.3	Low	4.0	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	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0018, the 7th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:14 UTC First seen by agentprime
31 Oct 2026, 14:14 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.