fix: harden against malformed ECDSA keys and empty header values

Reject nil ECDSA curves at JWS key validation and in raw sign/verify paths, and return errors instead of panicking when a header map entry has no values.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: yaronf

crypto_test.go

@@ -277,6 +277,7 @@ func TestNewJWSSigner(t *testing.T) {
 		{name: "ecdsa curve match", alg: jwa.ES256(), key: p256},
 		{name: "ecdsa public key", alg: jwa.ES256(), key: &p256.PublicKey, wantErr: true},
 		{name: "ecdsa curve mismatch", alg: jwa.ES384(), key: p256, wantErr: true},
+		{name: "ecdsa nil curve", alg: jwa.ES256(), key: ecdsa.PrivateKey{}, wantErr: true},
 		{name: "mldsa params match", alg: jwa.MLDSA44(), key: mldsa44},
 		{name: "mldsa public key", alg: jwa.MLDSA44(), key: mldsa44.Public().(*mldsa.PublicKey), wantErr: true},
 		{name: "mldsa params mismatch", alg: jwa.MLDSA65(), key: mldsa44, wantErr: true},

ecdsa.go

@@ -13,6 +13,9 @@ func ecdsaSignRaw(rd io.Reader, priv *ecdsa.PrivateKey, hash []byte) ([]byte, er
 	if priv == nil {
 		return nil, fmt.Errorf("nil private key")
 	}
+	if priv.Curve == nil {
+		return nil, fmt.Errorf("nil curve on private key")
+	}
 	r, s, err := ecdsa.Sign(rd, priv, hash)
 	if err != nil {
 		return nil, err
@@ -35,6 +38,9 @@ func ecdsaVerifyRaw(pub *ecdsa.PublicKey, hash []byte, sig []byte) (bool, error)
 	if pub == nil {
 		return false, fmt.Errorf("nil public key")
 	}
+	if pub.Curve == nil {
+		return false, fmt.Errorf("signature verification failed")
+	}
 	curve := pub.Params().Name
 	lr, ls, err := sigComponentLen(curve)
 	if err != nil {

ecdsa_test.go

@@ -78,6 +78,16 @@ func Test_ecdsaVerifyRaw(t *testing.T) {
 			want:    false,
 			wantErr: true,
 		},
+		{
+			name: "nil curve",
+			args: args{
+				pub:  &ecdsa.PublicKey{},
+				hash: bytes.Repeat([]byte{88}, 32),
+				sig:  make([]byte, 64),
+			},
+			want:    false,
+			wantErr: true,
+		},
 		{
 			name: "bad curve",
 			args: args{

jwskey.go

@@ -99,6 +99,9 @@ func validateECDSAKey(alg jwa.SignatureAlgorithm, key interface{}, signing bool)
 	if !signing && isPrivate {
 		return fmt.Errorf("algorithm %s requires an ECDSA public key for verification", alg)
 	}
+	if curve == nil {
+		return fmt.Errorf("algorithm %s: ECDSA key has nil curve", alg)
+	}
 	var want elliptic.Curve
 	switch alg {
 	case jwa.ES256():

signatures.go

@@ -254,6 +254,9 @@ func (message *parsedMessage) getRawHeader(hdr string, trailer bool) ([]string,
 	if !found {
 		return nil, fmt.Errorf("header %s not found", hdr)
 	}
+	if len(vv) == 0 {
+		return nil, fmt.Errorf("header %s has no values", hdr)
+	}
 	return vv, nil
 }
 
@@ -918,6 +921,9 @@ func applyPolicyCreated(psi *psiSignature, message parsedMessage, config VerifyC
 				if len(dateHdr) > 1 {
 					return fmt.Errorf("multiple Date headers")
 				}
+				if len(dateHdr) == 0 {
+					return fmt.Errorf("empty Date header")
+				}
 				date, err := http.ParseTime(dateHdr[0])
 				if err != nil {
 					return fmt.Errorf("cannot parse Date header: %w", err)

signatures_test.go

@@ -915,6 +915,14 @@ func TestVerifyDateWithin(t *testing.T) {
 	})
 }
 
+func TestGetRawHeaderEmptyValues(t *testing.T) {
+	msg := &parsedMessage{headers: http.Header{"x-custom": {}}}
+	_, err := msg.getRawHeader("x-custom", false)
+	if err == nil {
+		t.Fatal("expected error for header with no values")
+	}
+}
+
 // Same as TestCreated but using Message
 func TestMessageCreated(t *testing.T) {
 	testOnceWithConfig := func(t *testing.T, createdTime int64, verifyConfig *VerifyConfig, wantSuccess bool) {