Validate improper TLS RSA certificates early-on

network/peer/8192RSA_test.pem

@@ -0,0 +1,100 @@
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+-----END -----

network/peer/tls_config.go

@@ -4,8 +4,18 @@
 package peer
 
 import (
+	"crypto/rsa"
 	"crypto/tls"
+	"errors"
 	"io"
+
+	"github.com/ava-labs/avalanchego/staking"
+)
+
+var (
+	ErrNoCertsSent    = errors.New("no certificates sent by peer")
+	ErrEmptyCert      = errors.New("certificate sent by peer is empty")
+	ErrEmptyPublicKey = errors.New("no public key sent by peer")
 )
 
 // TLSConfig returns the TLS config that will allow secure connections to other
@@ -26,5 +36,29 @@ func TLSConfig(cert tls.Certificate, keyLogWriter io.Writer) *tls.Config {
 		InsecureSkipVerify: true, //#nosec G402
 		MinVersion:         tls.VersionTLS13,
 		KeyLogWriter:       keyLogWriter,
+		VerifyConnection:   ValidateRSACertificate,
+	}
+}
+
+// ValidateRSACertificate validates TLS certificates
+// with RSA public keys in the leaf of the certificate chain of the given connection state.
+func ValidateRSACertificate(cs tls.ConnectionState) error {
+	if len(cs.PeerCertificates) == 0 {
+		return ErrNoCertsSent
+	}
+
+	if cs.PeerCertificates[0] == nil {
+		return ErrEmptyCert
+	}
+
+	pk := cs.PeerCertificates[0].PublicKey
+
+	switch rsaKey := pk.(type) {
+	case *rsa.PublicKey:
+		return staking.ValidateRSAPublicKeyIsWellFormed(rsaKey)
+	case nil:
+		return ErrEmptyPublicKey
+	default:
+		return nil
 	}
 }

network/peer/tls_config_test.go

@@ -0,0 +1,94 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package peer_test
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/tls"
+	"crypto/x509"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/ava-labs/avalanchego/network/peer"
+	"github.com/ava-labs/avalanchego/staking"
+)
+
+func TestValidateRSACertificate(t *testing.T) {
+	for _, testCase := range []struct {
+		description string
+		input       func(t *testing.T) tls.ConnectionState
+		expectedErr error
+	}{
+		{
+			description: "Valid TLS cert",
+			input: func(t *testing.T) tls.ConnectionState {
+				key, err := rsa.GenerateKey(rand.Reader, 2048)
+				require.NoError(t, err)
+				x509Cert := makeRSACertAndKey(t, key)
+				return tls.ConnectionState{PeerCertificates: []*x509.Certificate{&x509Cert.cert}}
+			},
+		},
+		{
+			description: "No TLS certs given",
+			input: func(*testing.T) tls.ConnectionState {
+				return tls.ConnectionState{}
+			},
+			expectedErr: peer.ErrNoCertsSent,
+		},
+		{
+			description: "Empty certificate given by peer",
+			input: func(*testing.T) tls.ConnectionState {
+				return tls.ConnectionState{PeerCertificates: []*x509.Certificate{nil}}
+			},
+			expectedErr: peer.ErrEmptyCert,
+		},
+		{
+			description: "nil RSA key",
+			input: func(t *testing.T) tls.ConnectionState {
+				key, err := rsa.GenerateKey(rand.Reader, 2048)
+				require.NoError(t, err)
+
+				x509CertWithNilPK := makeRSACertAndKey(t, key)
+				x509CertWithNilPK.cert.PublicKey = (*rsa.PublicKey)(nil)
+				return tls.ConnectionState{PeerCertificates: []*x509.Certificate{&x509CertWithNilPK.cert}}
+			},
+			expectedErr: staking.ErrInvalidRSAPublicKey,
+		},
+		{
+			description: "No public key in the cert given",
+			input: func(t *testing.T) tls.ConnectionState {
+				key, err := rsa.GenerateKey(rand.Reader, 2048)
+				require.NoError(t, err)
+
+				x509CertWithNoPK := makeRSACertAndKey(t, key)
+				x509CertWithNoPK.cert.PublicKey = nil
+				return tls.ConnectionState{PeerCertificates: []*x509.Certificate{&x509CertWithNoPK.cert}}
+			},
+			expectedErr: peer.ErrEmptyPublicKey,
+		},
+		{
+			description: "EC cert",
+			input: func(t *testing.T) tls.ConnectionState {
+				ecKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+				require.NoError(t, err)
+
+				basicCert := basicCert()
+				certBytes, err := x509.CreateCertificate(rand.Reader, basicCert, basicCert, &ecKey.PublicKey, ecKey)
+				require.NoError(t, err)
+
+				ecCert, err := x509.ParseCertificate(certBytes)
+				require.NoError(t, err)
+				return tls.ConnectionState{PeerCertificates: []*x509.Certificate{ecCert}}
+			},
+		},
+	} {
+		t.Run(testCase.description, func(t *testing.T) {
+			require.Equal(t, testCase.expectedErr, peer.ValidateRSACertificate(testCase.input(t)))
+		})
+	}
+}