Bitcoin Mempool Swells to 89,031 Txs, Highest Since February Amid Coldcard Scare
Unconfirmed Bitcoin transactions climbed to 89,031, the highest since February, as a Coldcard firmware vulnerability reopened self-custody security debate.
Bitcoin’s mempool climbed to 89,031 unconfirmed transactions, the highest reading since February, in the wake of reports of an attack targeting Coldcard hardware wallets. The spike lands at a moment when self-custody security and steady ETF inflows are both under close scrutiny from on-chain watchers.
What the mempool number signals
A mempool backlog of this size means tens of thousands of transactions are sitting unconfirmed on the network, competing for block space. Congestion at this scale typically points to a surge in on-chain activity or defensive transaction batching by holders reacting to a security event, rather than routine payment flow.
For traders, a rising mempool queue is also a proxy for fee pressure: as unconfirmed transactions pile up, users compete more aggressively for the next block, pushing priority fees higher. The last comparable reading came in February, which puts the current backlog at a multi-month extreme.
Coldcard vulnerability reopens the custody debate
The congestion follows reports of an attack tied to Coldcard, one of the better-known air-gapped hardware wallets used by long-term Bitcoin holders for self-custody. Coverage of the incident points to a firmware-level flaw as the entry point, reigniting a long-running argument in the Bitcoin community over how much trust cold-storage users should place in closed or semi-closed firmware stacks.
Hardware wallets are marketed as the gold standard for keeping private keys offline and away from internet-connected attack surfaces. A firmware-level vulnerability undercuts that pitch directly, since it suggests the compromise sits inside the device’s own trusted code rather than in a user’s operational mistake.
ETF flows keep custody risk in focus
The timing matters because spot Bitcoin ETF inflows have kept institutional and retail exposure to BTC elevated, meaning more capital is routed through a mix of custodial and self-custody solutions than at almost any other point in Bitcoin’s history. Any credible doubt over hardware wallet integrity lands squarely on that debate, since it forces a comparison between the counterparty risk of ETF custodians and the technical risk of firmware running on consumer devices.
On-chain researchers will be watching whether the mempool backlog clears quickly as blocks absorb the queue, or whether it persists as a sign of sustained defensive activity — such as holders moving funds off potentially exposed wallets. Fee data and confirmation times over the coming days should clarify whether this was a short-lived spike or the start of a longer congestion cycle.
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