[ip6] add additional parse validation to Ip6::Address::FromString (#3830)

src/core/net/ip6_address.cpp

@@ -328,6 +328,8 @@ otError Address::FromString(const char *aBuf)
         VerifyOrExit(++count <= 4, error = OT_ERROR_PARSE);
     }
 
+    VerifyOrExit(colonp || dst == endp, error = OT_ERROR_PARSE);
+
     while (colonp && dst > colonp)
     {
         *endp-- = *dst--;

tests/unit/test_ip6_address.cpp

@@ -169,6 +169,26 @@ void TestIp6AddressFromString(void)
             OT_ERROR_PARSE
         },
 
+        // Invalid embedded IPv4 address.
+        {
+            ".",
+            {0},
+            OT_ERROR_PARSE
+        },
+
+        // Invalid embedded IPv4 address.
+        {
+            ":.",
+            {0},
+            OT_ERROR_PARSE
+        },
+
+        // Invalid embedded IPv4 address.
+        {
+            "::.",
+            {0},
+            OT_ERROR_PARSE
+        },
     };
 
     for (uint32_t index = 0; index < OT_ARRAY_LENGTH(testVectors); index++)