Post-Mortem: Coldcard Firmware Bug & The $70M PRNG Failure
Has anyone else reviewed the Galaxy Research report on the Coldcard incident? It’s absolutely chilling that an attacker drained 1,196 addresses for $70M in just 41 minutes. The root cause traces back to a March 2021 firmware update where seed generation was accidentally routed to a deterministic software PRNG instead of the hardware RNG.
If the entropy source is compromised or deterministic, the whole security model collapses. Here is a simplified Python snippet showing why relying on a deterministic seed (like a timestamp) creates a predictable key space that attackers can brute force:
import hashlib
import time
# Simulating the flaw: Deterministic seed based on timestamp
# In the real flaw, the PRNG state was predictable
timestamp = int(time.time())
weak_seed = hashlib.sha256(str(timestamp).encode()).hexdigest()
print(f"Deterministic Seed: {weak_seed}")
# If an attacker knows the timeframe of generation, they can reproduce this
attack_vector_seed = hashlib.sha256(str(timestamp - 10).encode()).hexdigest()
print(f"Attacker Guess Seed: {attack_vector_seed}")
For those of you managing hardware security modules (HSMs) or cold storage, what are your internal validation protocols? Are you manually verifying firmware signatures on air-gapped systems before updating, or just trusting the vendor's delivery mechanism?
This is why we always treat HSM and wallet firmware updates like a supply chain attack. We never update directly from the internet. Instead, we download the update on a sterile machine, verify the PGP signature against the vendor's public key (which we keep offline), and only then transfer it via USB to the device.
Here is the standard check we use before any deployment:
gpg --verify firmware-v4.2.0.sig firmware-v4.2.0.bin
If that signature fails, the device doesn't get touched. It adds overhead, but it prevents this exact class of 'bad build' errors.
From a SOC perspective, the velocity of that transaction sweep is the real indicator. We've started tuning our transaction monitoring rules to flag 'high-frequency outflows' from cold storage addresses, even if the amounts are small. If a dormant wallet suddenly initiates 5+ transactions in a minute, we freeze the bridge immediately.
For anyone using SIEM tools for crypto monitoring, a simple KQL rule like this helps catch the sweep:
BlockchainTransactions
| where EventType == "Transfer"
| summarize count() by bin(Timestamp, 1m), SourceAddress
| where count_ > 5
Better to flag a false positive than lose $70M.
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