In agreement of aether lane intelligence jumbly received many Pang fraud contract, they to investor acceptance, if you invest brushstroke aether lane to some agreement, it can be answered with a high return rate give you more aether money, however tall redound can in a steady stream absorbs capital to give the investor in front in order to feedback ceaselessly over there the investor from sequel.
Newest data of RatingToken of orgnaization of grade of big data of area piece catenary shows the basis, the whole world added 9552 agreement address newly in all on July 20, 2018, among them 317 are token intelligence agreement, what deserve attention additionally is same account established 7900 identical intelligence contract, use up Gas to expend 22 ETH in all, doubt is like batch of acting congenial compose to found.
ETH is a typical Pang token contract. This agreement can regard as fictitious money exchange, but only ETH and ETHX (ERC20 Token) trade right, trade every time, the Token allocation that has 5% gives whole platform already some Token hold person, because of this Token hold person during managing money, the poundage of the person that will earn new purchaser and old usu. in anticipation of or in order to bring about a fall in price directly. From ETHX agreement code can see, this agreement undertook expanding to TransferFrom function, transferFrom function undertakes Allowance limitation decides above all, called the TransferTokens function that defines oneself to finish next turn Zhang.
In TransferTokens function, do not be equal to agreement address when To account address, because be spent to From account specified number beforehand,had safe examination, because after this faces the Balance operation of From account,won't arise spill over.
When To account address is equal to agreement address, transfer Sell function, error is written as a result of code in Sell function, wrong write From into Msg.sender, spend to the forehead of Msg.sender undertook subtration is operated, and did not have safe examination before subtration is operated, because this is put,spilling over flaw.
Spill over to this to finish the attack of flaw, aggressor needs 2 account A, B, among them remaining sum of A account token is 0, b account token is 0.
1) A account calls Approve to turn partly to B accredit Zhang forehead is spent, hypothesis accredit forehead is spent for 1;
2) B account calls TransferFrom, turn from A account 1 unit token arrives intelligent agreement; When TransferFrom transfers Sell function, spark integer spills over, namely 0-1=2^255. B account falls for the circumstance of 0 in remaining sum obtained the biggest spent Token.
In catenary of ETHX agreement charge, aggressor used two account address, it is respectively:
0x423b1404f51a2cdae57e597181da0a4ca4492f30
0x17a6e289e16b788505903cc7cf966f5e33dd1b94
Above all, 0x17a6e289e16b788505903cc7cf966f5e33dd1b94 calls Approve to turn to 0x423b1404f51a2cdae57e597181da0a4ca4492f30 accredit Zhang forehead is spent, parameter Value=1.
Next, 0x423b1404f51a2cdae57e597181da0a4ca4492f30 calls TransferFrom method, transfer a Token to 0x1c98eea5fe5e15d77feeabc0dfcfad32314fd481 of ETHX agreement address from account 0x17a6e289e16b788505903cc7cf966f5e33dd1b94.
Before calling, balance(0x423b1404f51a2cdae57e597181da0a4ca4492f30)=0. After calling, the Balance(0x423b1404f51a2cdae57e597181da0a4ca4492f30)=2^255 after spilling over.
Monitoring platform shows the congener token agreement that has been atttacked expresses as follows:
Summary:
But actually investigate its are essential, so many intelligence agreement appears congener flaw, the digital token that its are a disorder rear issues the current situation. What remind even is, in the world of digital money, all sorts of flaw conceal among them, investor needs to make the psychological preparation that good flaw exposes at any time, in the meantime, the aptitude of platform oneself, also be the main factor that investor needs to consider carefully.
