Fix security vulnerability (#40)

Fixes a security vulnerability where a jwt token could potentially be validated having invalid string characters.

(cherry picked from commit a211650c6ae1cff6d7347d3e24070d65dcfb1122)
https://github.com/form3tech-oss/jwt-go/pull/14

Co-Authored-By: Giorgos Lampadakis <82932062+giorgos-f3@users.noreply.github.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

map_claims.go

@@ -34,27 +34,35 @@ func (m MapClaims) VerifyAudience(cmp string, req bool) bool {
 // Compares the exp claim against cmp.
 // If required is false, this method will return true if the value matches or is unset
 func (m MapClaims) VerifyExpiresAt(cmp int64, req bool) bool {
-	switch exp := m["exp"].(type) {
+	exp, ok := m["exp"]
+	if !ok {
+		return !req
+	}
+	switch expType := exp.(type) {
 	case float64:
-		return verifyExp(int64(exp), cmp, req)
+		return verifyExp(int64(expType), cmp, req)
 	case json.Number:
-		v, _ := exp.Int64()
+		v, _ := expType.Int64()
 		return verifyExp(v, cmp, req)
 	}
-	return !req
+	return false
 }
 
 // Compares the iat claim against cmp.
 // If required is false, this method will return true if the value matches or is unset
 func (m MapClaims) VerifyIssuedAt(cmp int64, req bool) bool {
-	switch iat := m["iat"].(type) {
+	iat, ok := m["iat"]
+	if !ok {
+		return !req
+	}
+	switch iatType := iat.(type) {
 	case float64:
-		return verifyIat(int64(iat), cmp, req)
+		return verifyIat(int64(iatType), cmp, req)
 	case json.Number:
-		v, _ := iat.Int64()
+		v, _ := iatType.Int64()
 		return verifyIat(v, cmp, req)
 	}
-	return !req
+	return false
 }
 
 // Compares the iss claim against cmp.
@@ -67,14 +75,18 @@ func (m MapClaims) VerifyIssuer(cmp string, req bool) bool {
 // Compares the nbf claim against cmp.
 // If required is false, this method will return true if the value matches or is unset
 func (m MapClaims) VerifyNotBefore(cmp int64, req bool) bool {
-	switch nbf := m["nbf"].(type) {
+	nbf, ok := m["nbf"]
+	if !ok {
+		return !req
+	}
+	switch nbfType := nbf.(type) {
 	case float64:
-		return verifyNbf(int64(nbf), cmp, req)
+		return verifyNbf(int64(nbfType), cmp, req)
 	case json.Number:
-		v, _ := nbf.Int64()
+		v, _ := nbfType.Int64()
 		return verifyNbf(v, cmp, req)
 	}
-	return !req
+	return false
 }
 
 // Validates time based claims "exp, iat, nbf".

map_claims_test.go

@@ -66,3 +66,37 @@ func TestVerifyAud(t *testing.T) {
 		})
 	}
 }
+
+func TestMapclaimsVerifyIssuedAtInvalidTypeString(t *testing.T) {
+	mapClaims := MapClaims{
+		"iat": "foo",
+	}
+	want := false
+	got := mapClaims.VerifyIssuedAt(0, false)
+	if want != got {
+		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, got)
+	}
+}
+
+func TestMapclaimsVerifyNotBeforeInvalidTypeString(t *testing.T) {
+	mapClaims := MapClaims{
+		"nbf": "foo",
+	}
+	want := false
+	got := mapClaims.VerifyNotBefore(0, false)
+	if want != got {
+		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, got)
+	}
+}
+
+func TestMapclaimsVerifyExpiresAtInvalidTypeString(t *testing.T) {
+	mapClaims := MapClaims{
+		"exp": "foo",
+	}
+	want := false
+	got := mapClaims.VerifyExpiresAt(0, false)
+
+	if want != got {
+		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, got)
+	}
+}