uTLS has a fingerprint vulnerability from GREASE ECH mismatch for Chrome parrots

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.3 · 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 · score source

EPSS

• CVE-2026-27017: 0.18% estimated exploitation activity in the next 30 days; percentile 7.05 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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: HelloChrome120, HelloChrome120PQ, HelloChrome131, HelloChrome133 Fix commit: 24bd1e05a788c1add7f3037f4532ea552b2cee07 Thanks to telegram @acgdaily for reporting this issue.

Published by the source

18 Feb 2026, 22:33 UTC

Last modified by the source

27 Feb 2026, 20:37 UTC

Source last checked

26 Oct 2026, 15:14 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-7m29-f4hw-g2vx

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# Patch Next advisory brief: CVE-2026-27017

Advisory: uTLS has a fingerprint vulnerability from GREASE ECH mismatch for Chrome parrots
IDs: CVE-2026-27017, GHSA-7m29-f4hw-g2vx
Record: https://patchnext.com/advisories/cve-2026-27017 (revision 1, source checked 26 Oct 2026, 15:14 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/refraction-networking/utls 1.8.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/refraction-networking/utls: affected >= 1.6.0, < 1.8.1; fixed in 1.8.1

## Suggested inspection (read-only)
- Go github.com/refraction-networking/utls: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/refraction-networking/utls.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-7m29-f4hw-g2vx (GitHub-reviewed advisory GHSA-7m29-f4hw-g2vx lists affected ranges: Go github.com/refraction-networking/utls >=1.6.0 <1.8.1)

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