How Does a Preimage Attack Relate to the Security of Bitcoin’s Blockchain?

Bitcoin uses the SHA-256 hash function extensively, notably in mining and transaction IDs. A successful preimage attack on SHA-256 would allow an attacker to reverse a transaction ID hash to find the original transaction data.

More critically, it could allow an attacker to find a valid block header input (preimage) for a given target hash, bypassing the computational work of mining. This would severely undermine the integrity and proof-of-work mechanism of the entire blockchain.