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National Vulnerability Database

National Vulnerability Database

NVD

National Vulnerability Database
  1. Vulnerabilities

CVE-2026-26994 Detail

Description

uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprinting resistance while still using it for the handshake. In versions 1.6.7 and below, uTLS did not implement the TLS 1.3 downgrade protection mechanism specified in RFC 8446 Section 4.1.3 when using a uTLS ClientHello spec. This allowed an active network adversary to downgrade TLS 1.3 connections initiated by a uTLS client to a lower TLS version (e.g., TLS 1.2) by modifying the ClientHello message to exclude the SupportedVersions extension, causing the server to respond with a TLS 1.2 ServerHello (along with a downgrade canary in the ServerHello random field). Because uTLS did not check the downgrade canary in the ServerHello random field, clients would accept the downgraded connection without detecting the attack. This attack could also be used by an active network attacker to fingerprint uTLS connections. This issue has been fixed in version 1.7.0.


Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NIST CVSS score
NIST: NVD
N/A
NVD assessment not yet provided.

References to Advisories, Solutions, and Tools

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URL Source(s) Tag(s)
https://github.com/refraction-networking/utls/commit/f8892761e2a4d29054264651d3a86fda83bc83f9 GitHub, Inc. Patch 
https://github.com/refraction-networking/utls/issues/181 GitHub, Inc. Issue Tracking 
https://github.com/refraction-networking/utls/pull/337 GitHub, Inc. Issue Tracking  Patch 
https://github.com/refraction-networking/utls/security/advisories/GHSA-pmc3-p9hx-jq96 GitHub, Inc. Patch  Vendor Advisory 

Weakness Enumeration

CWE-ID CWE Name Source
CWE-693 Protection Mechanism Failure GitHub, Inc.  

Known Affected Software Configurations Switch to CPE 2.2

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Change History

2 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2026-26994
NVD Published Date:
02/19/2026
NVD Last Modified:
02/20/2026
Source:
GitHub, Inc.