CVE-2026-26994

MEDIUM EPSS 18.3%
Published Feb 20, 20264mo ago · Modified Jun 17, 20262w ago
6.5 CVSS 3.1
Medium
Find Similar
Published Feb 20, 2026 4mo ago
Last Modified Jun 17, 2026 2w ago

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.

CVSS Details

Base Score
6.5
Exploitability
3.9
Impact
2.5
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality Low
Integrity Low
Availability None

Threat Intelligence

EPSS Exploit Probability
18.3% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 1

CWE-693

Affected Products 1

VendorProductVersionRange
refraction-networkingutls* <1.7.0

References 4

  • github.com https://github.com/refraction-networking/utls/commit/f8892761e2a4d29054264651d3a86fda83bc83f9
    Patch
  • github.com https://github.com/refraction-networking/utls/issues/181
    Issue Tracking
  • github.com https://github.com/refraction-networking/utls/pull/337
    Issue TrackingPatch
  • github.com https://github.com/refraction-networking/utls/security/advisories/GHSA-pmc3-p9hx-jq96
    PatchVendor Advisory

Remediation

  • github.com https://github.com/refraction-networking/utls/commit/f8892761e2a4d29054264651d3a86fda83bc83f9
    Patch
  • github.com https://github.com/refraction-networking/utls/pull/337
    Issue TrackingPatch
  • github.com https://github.com/refraction-networking/utls/security/advisories/GHSA-pmc3-p9hx-jq96
    PatchVendor Advisory