> how is it possible that in Block B it has the same transaction twice? I would have thought this was something that violated validation rules 

That’s exactly what the fix for CVE-2012-2459 addressed. After Bitcoin 0.6.1, core rejects blocks with duplicate txs.

commit for the fix in Core

https://github.com/bitcoin/bitcoin/commit/be8651dde7b59e50e8c443da71c706667803d06d

bitcoin_devs

> This is really helpful! I love these explainers of CVEs.

will make some explainers for the CVEs disclosed today 

https://bitcoincore.org/en/2025/10/24/disclose-cve-2025-46598/

This is really helpful! I love these explainers of CVEs.

One question: how is it possible that in Block B it has the same transaction twice? I would have thought this was something that violated validation rules (I'm assuming both TX3s spend the same utxo to the same addresses)?

bitcoin

⚠️ CVE-2012-2459 explained

This is really helpful! I love these explainers of CVEs. 

One question: how is it possible that in Block B it has the same transaction twice? I would have thought this was something that violated validation rules (I'm assuming both TX3s spend the same utxo to the same addresses)?