6.5

CVE-2026-26994: uTLS ServerHellos are accepted without checking TLS 1.3 downgrade canaries

Analyzed
AliasesUBUNTU-CVE-2026-26994DEBIAN-CVE-2026-26994CGA-59qq-82rh-hr4h
Published 20-02-2026Last modified 20-02-2026

Vulnerability summary

CVE-2026-26994 is a medium (CVSS 6.5) Protection Mechanism Failure vulnerability in refraction-networking utls. EPSS estimates a 0.30% chance of exploitation in the next 30 days, higher than 22.9% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 6.5, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
6.5/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.30%
0%100%
Low · -0.08 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 0 · Related 1
CGA-9W9M-3Q9J-7399

Timeline

  1. 20-02-2026
    PublishedVulnerability first disclosed.
  2. 20-02-2026
    Last modifiedVulnerability information updated.

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 metrics

7 scores · 7 sources · 1 version

EPSS trend

Probability

0.30%

Chance of exploitation in the next 30 days

Percentile

23%

Versus all other CVEs

30-day change

Decrease -0.08 pp

From 0.38% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Chainguard1 product
  • nuclei< 3.4.2-r2
Debian1 product
  • golang-refraction-networking-utlsAll versions (No fix recorded)
Github.com/refraction-networking1 product
  • utls< 1.7.0 | ≥ 1.0.0, < 1.7.0
Refraction-networking1 product
Ubuntu1 product
  • golang-refraction-networking-utlsAll versions (No fix recorded)
Wolfi1 product
  • nuclei< 3.4.2-r2

6 vendors · 6 products

References

11 links
Show all 11 references