How are transactions verified in Blockchain?

Question

Programming

It is not clear how the transaction is actually verified.
Let's say we have a hash tree
root
abcd efgd
/\ /\
ab cd ef gd
/\ /\ /\ /\
abcdefgd
How, for example, is transaction verification a? How do cd and efgd get the necessary hashes? Are they recalculated or stored somewhere and simply retrieved from memory?
And I would also like to know about the CVE-2012-2459 vulnerability, how the attackers used it and how this problem was solved?

Answer 1

Blockchain is a list, not a tree.
And verification occurs by digital signature. Each transaction must be signed with a private key.

Answer 2

The recipient-recipient must know that none of the previous owners signed a transaction that
precedes the one in the chain of the coin sent to him.
Nodes accept the block only if all transactions in it are correct and do not use
funds already spent. The timestamp in the blockchain shows that at the moment specific data existed and therefore got into the hash of the block.
it's not clear what you mean by "cd and efgd"
I can assume that this is part of the Merkele tree, and by the way is related to the vulnerability you mentioned. If my memory serves me, then the vulnerability is related to the duplication of transactions in one block, and the unchanged root of the merkel. And the problem was solved very simply, a check for repeated transactions in the received block was introduced.