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fix(webauthncose): potential nil ptr in ec unmarshal #101

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merged 1 commit into from
Jan 29, 2023
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fix(webauthncose): potential nil ptr in ec unmarshal #101

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fix(webauthncose): potential nil ptr in ec unmarshal 
This fixes a potential nil ptr panic in the ParseFIDOPublicKey function.
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@james-d-elliott
james-d-elliott committed Jan 29, 2023
commit 859acd074d927f81ce9dd3bc2333cfe9db467e17
31 changes: 18 additions & 13 deletions protocol/webauthncose/webauthncose.go
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ import (
"crypto/x509"
"encoding/asn1"
"encoding/pem"
"fmt"
"hash"
"math/big"

Expand Down Expand Up @@ -183,9 +184,13 @@ func ParsePublicKey(keyBytes []byte) (interface{}, error) {
}

// ParseFIDOPublicKey is only used when the appID extension is configured by the assertion response.
func ParseFIDOPublicKey(keyBytes []byte) (EC2PublicKeyData, error) {
func ParseFIDOPublicKey(keyBytes []byte) (data EC2PublicKeyData, err error) {
x, y := elliptic.Unmarshal(elliptic.P256(), keyBytes)

if x == nil || y == nil {
return data, fmt.Errorf("elliptic unmarshall returned a nil value")
}

return EC2PublicKeyData{
PublicKeyData: PublicKeyData{
Algorithm: int64(AlgES256),
Expand Down Expand Up @@ -288,13 +293,13 @@ func (k *EC2PublicKeyData) TPMCurveID() tpm2.EllipticCurve {

func VerifySignature(key interface{}, data []byte, sig []byte) (bool, error) {

switch key := key.(type) {
switch k := key.(type) {
case OKPPublicKeyData:
return key.Verify(data, sig)
return k.Verify(data, sig)
case EC2PublicKeyData:
return key.Verify(data, sig)
return k.Verify(data, sig)
case RSAPublicKeyData:
return key.Verify(data, sig)
return k.Verify(data, sig)
default:
return false, ErrUnsupportedKey
}
Expand All @@ -305,11 +310,11 @@ func DisplayPublicKey(cpk []byte) string {
if err != nil {
return "Cannot display key"
}
switch parsedKey := parsedKey.(type) {
switch k := parsedKey.(type) {
case RSAPublicKeyData:
rKey := &rsa.PublicKey{
N: big.NewInt(0).SetBytes(parsedKey.Modulus),
E: int(uint(parsedKey.Exponent[2]) | uint(parsedKey.Exponent[1])<<8 | uint(parsedKey.Exponent[0])<<16),
N: big.NewInt(0).SetBytes(k.Modulus),
E: int(uint(k.Exponent[2]) | uint(k.Exponent[1])<<8 | uint(k.Exponent[0])<<16),
}
data, err := x509.MarshalPKIXPublicKey(rKey)
if err != nil {
Expand All @@ -322,7 +327,7 @@ func DisplayPublicKey(cpk []byte) string {
return string(pemBytes)
case EC2PublicKeyData:
var curve elliptic.Curve
switch COSEAlgorithmIdentifier(parsedKey.Algorithm) {
switch COSEAlgorithmIdentifier(k.Algorithm) {
case AlgES256:
curve = elliptic.P256()
case AlgES384:
Expand All @@ -334,8 +339,8 @@ func DisplayPublicKey(cpk []byte) string {
}
eKey := &ecdsa.PublicKey{
Curve: curve,
X: big.NewInt(0).SetBytes(parsedKey.XCoord),
Y: big.NewInt(0).SetBytes(parsedKey.YCoord),
X: big.NewInt(0).SetBytes(k.XCoord),
Y: big.NewInt(0).SetBytes(k.YCoord),
}
data, err := x509.MarshalPKIXPublicKey(eKey)
if err != nil {
Expand All @@ -347,11 +352,11 @@ func DisplayPublicKey(cpk []byte) string {
})
return string(pemBytes)
case OKPPublicKeyData:
if len(parsedKey.XCoord) != ed25519.PublicKeySize {
if len(k.XCoord) != ed25519.PublicKeySize {
return "Cannot display key"
}
var oKey ed25519.PublicKey = make([]byte, ed25519.PublicKeySize)
copy(oKey, parsedKey.XCoord)
copy(oKey, k.XCoord)
data, err := marshalEd25519PublicKey(oKey)
if err != nil {
return "Cannot display key"
Expand Down