Pinning Attacks Pinning = an attacker publishes a tx that blocks your tx from confirming by attaching as a descendant chain that exhausts mempool descendant limits or replacement-fee budgets. Classic pinning You publish parent P (commitment, HTLC-timeout, etc.). Attacker publishes child C spending P's output: - C has very low fee rate but has 24+ unconfirmed ancestors/ descendants of its own (Tx graph). - Mempool admits C; descendant chain reaches policy limits. - Now ANY new descendant of P is rejected: descendant limit exceeded. - You can't CPFP P; you can't RBF (your replacement would conf…