Withdraw Account can be empty

Describe The Bug
In distribution module, delegator's withdraw Account can be empty
when the event like unbonding or redelegation happen, rewarding coins will be burn.

In other words, Adversary can burn coins by a malicious transaction without the signature of coin's creator.

Code Snippets
validateBasic of setWithdrawAccount hasn't be implemented.
malicious transactions with empty withdrawAccount will be preformed normally.

setWithdrawAccount structs look like this

type MsgSetWithdrawAccountIdData struct {
	DelegatorAccountid chainType.AccountID 
	WithdrawAccountid  chainType.AccountID 
}

Input/Output

1. input command line like this:
   ./build/ktscli tx kudistribution set-withdraw kratos --keyring-backend test --chain-id testing --home ./testing/cli/ --from kratos

2. output a normally successful response

To Reproduce

1. found func GetCmdSetWithdrawAddr(cdc *codec.Codec) *cobra.Command { in x/distribution/client/cli.go
   modify cobra.ExactArgs(2) into cobra.ExactArgs(1)
   modify withdrawAccId, err := chainType.NewAccountIDFromStr(args[0]) into
   withdrawAccId, err := chainType.NewAccountIDFromStr("")

2.remake ktscli

3.run command like this ./build/ktscli tx kudistribution set-withdraw kratos --keyring-backend test --chain-id testing --home ./testing/cli/ --from kratos
and we can see the normal response.

4. finally check your withdraw addr with command ./build/ktscli query kudistribution whithdraw-addr kratos
   

as above, we set the withdrawAddr to empty.

Expected Behavior
kratos need intact ValidateBasic function which be called in the AnteHandler for distribution module

Desktop

• OS: MacOS catalina 10.15.

Additional Context
the difference between issue#14 to issue#15 is that there wasn't any implementation of ValidateBasic for distribution in issue#15 at all.

Contact Information
congfei.li@chaitin.com

[Pisces-Anjou]

Hi

Thanks for your submission.
We have tested the issue you mentioned and did reproduce it.
This is a valid vulnerability. After evaluation, this vulnerability has been graded as P3.
Please pay attention to the announcement and your email to get your rewards.
Thanks for your attention and contribution. Please keep trying and help us improve our chain.

Regards
KuChain Team