CVE-2026-27017
published 2026-02-20CVE-2026-27017: 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…
PriorityP427medium5.3CVSS 3.1
AVNACLPRNUINSUCLINAN
EPSS
0.16%
5.6th percentile
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.
Affected
4 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| debian | golang-refraction-networking-utls | — | — |
| github.com | refraction-networking_utls | >= 1.6.0 < 1.8.1 | 1.8.1 |
| refraction-networking | utls | — | — |
| refraction-networking | utls | >= 1.6.0 < 1.8.1 | 1.8.1 |
CVSS provenance
nvdv3.15.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
nvdv4.02.3LOWCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
osv2.3LOW
vendor_debian2.3LOW
Stop checking back — get the weekly exploitation signal.
Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.
OSV
Fingerprint vulnerability in uTLS from GREASE ECH mismatch for Chrome parrots in github.com/refraction-networking/utls
osv·2026-02-24
CVE-2026-27017 Fingerprint vulnerability in uTLS from GREASE ECH mismatch for Chrome parrots in github.com/refraction-networking/utls
Fingerprint vulnerability in uTLS from GREASE ECH mismatch for Chrome parrots in github.com/refraction-networking/utls
Fingerprint vulnerability in uTLS from GREASE ECH mismatch for Chrome parrots in github.com/refraction-networking/utls
OSV
CVE-2026-27017: uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprinting resistance while still using it for the handshake
osv·2026-02-20·CVSS 2.3
CVE-2026-27017 [LOW] CVE-2026-27017: uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprinting resistance while still using it for the handshake
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 GREAS
GHSA
uTLS has a fingerprint vulnerability from GREASE ECH mismatch for Chrome parrots
ghsa·2026-02-18
CVE-2026-27017 [LOW] CWE-1240 uTLS has a fingerprint vulnerability from GREASE ECH mismatch for Chrome parrots
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
OSV
uTLS has a fingerprint vulnerability from GREASE ECH mismatch for Chrome parrots
osv·2026-02-18
CVE-2026-27017 [LOW] uTLS has a fingerprint vulnerability from GREASE ECH mismatch for Chrome parrots
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
Debian
CVE-2026-27017: golang-refraction-networking-utls - uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprintin...
vendor_debian·2026·CVSS 2.3
CVE-2026-27017 [LOW] CVE-2026-27017: golang-refraction-networking-utls - uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprintin...
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 GREAS
No detection rules found.
No public exploits indexed.
2026-02-20
Published