Miggo Logo
Miggo Vulnerability Database
→
GHSA-pmc3-p9hx-jq96

GHSA-pmc3-p9hx-jq96: uTLS ServerHellos are accepted without checking TLS 1.3 downgrade canaries

6.5

CVSS Score
3.1

Basic Information

CVE ID
-
GHSA ID
GHSA-pmc3-p9hx-jq96
EPSS Score
-
CWE
CWE-693
Published
4/23/2025
Updated
4/23/2025
KEV Status
No
Technology
TechnologyGo

Technical Details

CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Package NameEcosystemVulnerable VersionsFirst Patched Version
github.com/refraction-networking/utlsgo< 1.7.01.7.0

Vulnerability Intelligence
Miggo AIMiggo AI

Miggo AIRoot Cause Analysis

The vulnerability description clearly states that utls did not implement the TLS 1.3 downgrade protection mechanism, specifically by not checking the downgrade canary in the ServerHello random field. The provided commit f8892761e2a4d29054264651d3a86fda83bc83f9 shows modifications to the u_handshake_client.go file. The patch introduces a check for these downgrade canaries within the clientHandshake method of the UConn struct. This function is where the ServerHello is processed. The absence of this check before the patch made this function vulnerable to the described downgrade attack. Therefore, (*UConn).clientHandshake is identified as the vulnerable function.

Vulnerable functions

Only Mi**o us*rs **n s** t*is s**tion

WAF Protection Rules

WAF Rule

### **s*ription ***or* v*rsion *.*.*, utls *i* not impl*m*nt t** TLS *.* *own*r*** prot**tion m****nism sp**i*i** in R** **** S**tion *.*.* w**n usin* * utls *li*nt**llo sp**. T*is *llow** *n **tiv* n*twork **v*rs*ry to *own*r*** TLS *.* *onn**tions

Reasoning

T** vuln*r**ility **s*ription *l**rly st*t*s t**t utls *i* not impl*m*nt t** TLS *.* *own*r*** prot**tion m****nism, sp**i*i**lly *y not ****kin* t** *own*r*** **n*ry in t** S*rv*r**llo r*n*om *i*l*. T** provi*** *ommit `*****************************