COLDCARD RNG Flaw Linked to $88.6M Bitcoin Theft
A firmware bug in COLDCARD hardware wallets allowed attackers to recover wallet seeds and steal an estimated 1,367 BTC, worth about $88.6 million, from 4,585 Bitcoin addresses.
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Affected COLDCARD firmware was supposed to use the STM32 hardware RNG (Random Number Generator) when creating wallet seeds. Instead, an integration error caused it to fall back to MicroPython’s deterministic Yasmarang pseudorandom number generator.
The fallback was seeded using values such as:
Device identifiers
System timing data
Real-time clock values
Previous RNG state
These values are not secure sources of cryptographic randomness. An attacker could generate possible wallet seeds offline, derive the related Bitcoin addresses, and compare them against funded addresses on the public blockchain. Once a match was found, the attacker could derive the private keys and move the funds.
The transaction pattern supports the theory of an automated attack. Many wallets were swept using the same unusually high fee rate, with no change outputs. The flaw affected several COLDCARD models and firmware versions, including older Mk2 and Mk3 devices and some Mk4, Mk5, and Q firmware releases. Fixed firmware is now available, but updating alone does not protect a seed that was generated by vulnerable firmware.
Affected users should:
Install the fixed firmware
Generate a new seed
Verify the new wallet address
Move funds to the new wallet
Sources:
Block Bitcoin Engineering: Predictable RNG Fallback and 32-Bit Reseed in COLDCARD Firmware
https://engineering.block.xyz/blog/predictable-rng-fallback-and-32-bit-reseed-in-coldcard-firmware
Coinkite: COLDCARD Security Advisory
https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/
BleepingComputer: COLDCARD Wallet RNG Flaw Likely Linked to $88 Million Bitcoin Theft
https://www.bleepingcomputer.com/news/security/coldcard-wallet-rng-flaw-likely-linked-to-88-million-bitcoin-theft/
Galaxy Research: Initial On-Chain Analysis of the Wallet Sweeps
https://x.com/glxyresearch/status/2083181683067506899