Skip to main content

Boteraser | Website and Server Security Solutions

🛡️ CVE-2026-27017 — utls

🟡 CVSS 5.3 — Medium ✅ No Known Exploit CWE-1240 NVD
5.3
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality low, integrity none, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: Low — limited, and the attacker does not choose what is affected.
  • Integrity impact: None.
  • Availability impact: None.

Weakness class

CVE-2026-27017 is classified as CWE-1240: Use of a Cryptographic Primitive with a Risky Implementation. To fulfill the need for a cryptographic primitive, the product implements a cryptographic algorithm using a non-standard, unproven, or disallowed/non-compliant cryptographic implementation.

Affected software

CVE-2026-27017 is recorded against 2 packages.

  • github.com/refraction-networking/utls
  • utls (from 1.6.0 up to 1.8.1)

Timeline and source

Published on 18 February 2026 and last revised on 28 February 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Package)
github.com (Web)
pkg.go.dev (Web)

Other advisories for this package

github.com/refraction-networking/utls has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-1240: Use of a Cryptographic Primitive with a Risky Implementation) in other software:

CVE-2026-27017 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity LOW
CVSS Score 5.3
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
CWE CWE-1240
Public Exploit ✅ No
Source NVD
Published 2026-02-18
Updated 2026-08-20
Modified 2026-02-28

Affected Packages

Software From version Fixed in
github.com/refraction-networking/utls — —
utls 1.6.0 1.8.1

Similar Threats

Vulnerability Monitoring

Track new vulnerabilities in utls

CVE-2026-27017 is rated CVSS 5.3 Medium. BotEraser monitors your WordPress installation and notifies you when software you use appears in our vulnerability database.

Set Up Free Alerts →

No credit card required  ·  Results in minutes

ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

Browse related advisories

All advisoriesCVECVE 2026
✓