I think it's more privacy rather than security problem.
Thanks to SPV mechanism, all malicious server could do are refusing some service (e.g. return transaction information and broadcast signed transaction) and giving malicious message (if you use older version of Electrum).
people should seriously stop referring to Electrum nodes as "servers" because even though it is a correct term to use but it is very misleading. these aren't servers like other light weight wallets might use. you don't connect to get a balance! these are actual nodes which you connect to, receive block headers, your transactions AND merkle trees to verify whether the received transaction and its confirmation status (the block number) was correct.
that means Electrum nodes can NOT lie about a transaction being confirmed. the only thing they can lie about is saying it is unconfirmed which can not cause any harm.