refraction-networking utls up to 1.8.0 cryptographic primitive risky implementation

Summaryinfo

A vulnerability was found in refraction-networking utls up to 1.8.0. It has been classified as problematic. The impacted element is an unknown function. Performing a manipulation results in cryptographic primitive risky implementation. This vulnerability is cataloged as CVE-2026-27017. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as problematic, was found in refraction-networking utls up to 1.8.0. This affects an unknown code block. The manipulation with an unknown input leads to a cryptographic primitive risky implementation vulnerability. CWE is classifying the issue as CWE-1240. 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. This is going to have an impact on confidentiality. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-27017 since 02/17/2026. The exploitability is told to be difficult. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available.

The vulnerability scanner Nessus provides a plugin with the ID 299829 (Linux Distros Unpatched Vulnerability : CVE-2026-27017), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 1.8.1 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (299829). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

• refraction-networking

Name

• utls

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8.0

Website

• Product: https://github.com/refraction-networking/utls/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

Discussion