CVE-2026-26994

6.5 MEDIUM 0.3% exploit odds Fix listed Other Server

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. Limited direct impact.
Exploit odds: 0.3% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-02-20 03:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-06-17 10:26 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.3% in the next 30 days (EPSS).
Severity: 6.5 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-02-20 03:16 UTC
Last modified: 2026-06-17 10:26 UTC
Exploit probability: 0.3% · EPSS, next 30 days
Weakness: CWE-693
Record status: Analyzed

Affected

refraction-networking Utls < 1.7.0

Attack profile CVSS 3.1 · 6.5

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: None

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Is it in your code?

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Fix and advisories

References

NVD record · CVE.org record