GO-2025-3638

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Source

https://pkg.go.dev/vuln/GO-2025-3638

Import Source

https://vuln.go.dev/ID/GO-2025-3638.json

JSON Data

https://api.osv.dev/v1/vulns/GO-2025-3638

Aliases

GHSA-pmc3-p9hx-jq96

Published

2025-04-24T18:13:59Z

Modified

2025-04-24T18:42:11.304397Z

Summary

ServerHellos are accepted without checking TLS 1.3 downgrade canaries in github.com/refraction-networking/utls

Details

Before version 1.7.0, 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.

Database specific

{
    "review_status": "REVIEWED",
    "url": "https://pkg.go.dev/vuln/GO-2025-3638"
}

References

Affected packages

Go / github.com/refraction-networking/utls

Package

Name: github.com/refraction-networking/utls; View open source insights on deps.dev
Purl: pkg:golang/github.com/refraction-networking/utls

Affected ranges

Type: SEMVER
Events: Introduced

1.0.0

Fixed

1.7.0

Ecosystem specific

{
    "imports": [
        {
            "path": "github.com/refraction-networking/utls",
            "symbols": [
                "Conn.Handshake",
                "Conn.HandshakeContext",
                "Conn.Read",
                "Conn.Write",
                "Dial",
                "DialWithDialer",
                "Dialer.Dial",
                "Dialer.DialContext",
                "QUICConn.Start",
                "Roller.Dial",
                "UConn.Handshake",
                "UConn.HandshakeContext",
                "UConn.Read",
                "UConn.Write",
                "UConn.clientHandshake",
                "UQUICConn.HandleData",
                "UQUICConn.Start"
            ]
        }
    ]
}