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6.5
MEDIUM CVSS 3.1
CVE-2026-26994
uTLS ServerHellos are accepted without checking TLS 1.3 downgrade canaries
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.

INFO

Published Date :

Feb. 20, 2026, 3:16 a.m.

Last Modified :

Feb. 20, 2026, 7:20 p.m.

Remotely Exploit :

Yes !

Source :

[email protected]
Affected Products

The following products are affected by CVE-2026-26994 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Refraction-networking utls
: Total Affected Vendor : 1 | Products : 1
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 3.1 MEDIUM [email protected]
Solution
Update uTLS to version 1.7.0 or later to fix TLS downgrade attacks and fingerprinting.
  • Update uTLS to version 1.7.0.
  • Ensure TLS 1.3 downgrade protection is enabled.
  • Validate server configurations for TLS 1.3.
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2026-26994.

URL Resource
https://github.com/refraction-networking/utls/commit/f8892761e2a4d29054264651d3a86fda83bc83f9 Patch
https://github.com/refraction-networking/utls/issues/181 Issue Tracking
https://github.com/refraction-networking/utls/pull/337 Issue Tracking Patch
https://github.com/refraction-networking/utls/security/advisories/GHSA-pmc3-p9hx-jq96 Patch Vendor Advisory
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-26994 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-26994 weaknesses.

CAPEC-1: Accessing Functionality Not Properly Constrained by ACLs Accessing Functionality Not Properly Constrained by ACLs CAPEC-17: Using Malicious Files Using Malicious Files CAPEC-20: Encryption Brute Forcing Encryption Brute Forcing CAPEC-22: Exploiting Trust in Client Exploiting Trust in Client CAPEC-36: Using Unpublished Interfaces or Functionality Using Unpublished Interfaces or Functionality CAPEC-51: Poison Web Service Registry Poison Web Service Registry CAPEC-57: Utilizing REST's Trust in the System Resource to Obtain Sensitive Data Utilizing REST's Trust in the System Resource to Obtain Sensitive Data CAPEC-59: Session Credential Falsification through Prediction Session Credential Falsification through Prediction CAPEC-65: Sniff Application Code Sniff Application Code CAPEC-74: Manipulating State Manipulating State CAPEC-87: Forceful Browsing Forceful Browsing CAPEC-107: Cross Site Tracing Cross Site Tracing CAPEC-127: Directory Indexing Directory Indexing CAPEC-237: Escaping a Sandbox by Calling Code in Another Language Escaping a Sandbox by Calling Code in Another Language CAPEC-477: Signature Spoofing by Mixing Signed and Unsigned Content Signature Spoofing by Mixing Signed and Unsigned Content CAPEC-480: Escaping Virtualization Escaping Virtualization CAPEC-668: Key Negotiation of Bluetooth Attack (KNOB) Key Negotiation of Bluetooth Attack (KNOB)

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2026-26994 vulnerability anywhere in the article.

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2026-26994 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • Initial Analysis by [email protected]

    Feb. 20, 2026

    Action Type Old Value New Value
    Added CPE Configuration OR *cpe:2.3:a:refraction-networking:utls:*:*:*:*:*:go:*:* versions up to (excluding) 1.7.0
    Added Reference Type GitHub, Inc.: https://github.com/refraction-networking/utls/commit/f8892761e2a4d29054264651d3a86fda83bc83f9 Types: Patch
    Added Reference Type GitHub, Inc.: https://github.com/refraction-networking/utls/issues/181 Types: Issue Tracking
    Added Reference Type GitHub, Inc.: https://github.com/refraction-networking/utls/pull/337 Types: Issue Tracking, Patch
    Added Reference Type GitHub, Inc.: https://github.com/refraction-networking/utls/security/advisories/GHSA-pmc3-p9hx-jq96 Types: Patch, Vendor Advisory
  • New CVE Received by [email protected]

    Feb. 20, 2026

    Action Type Old Value New Value
    Added 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.
    Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
    Added CWE CWE-693
    Added Reference https://github.com/refraction-networking/utls/commit/f8892761e2a4d29054264651d3a86fda83bc83f9
    Added Reference https://github.com/refraction-networking/utls/issues/181
    Added Reference https://github.com/refraction-networking/utls/pull/337
    Added Reference https://github.com/refraction-networking/utls/security/advisories/GHSA-pmc3-p9hx-jq96
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.
Vulnerability Scoring Details
Base CVSS Score: 6.5
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact