Executive Summary

Coldcard is a widely trusted hardware wallet designed to secure Bitcoin private keys. During our independent review of the firmware source code, we discovered a flaw that has serious implications for the security of stored assets. Out of respect for the responsible disclosure process, the technical attack path is being kept confidential until a fix is available.

Importantly, this advisory does not mean Coldcard is unsafe to use if handled carefully. Instead, it highlights the importance of strict operational security when using hardware wallets. Until a firmware update is released, users should take immediate steps to reduce exposure.

Potential Risks

Based on our assessment, exploitation of this vulnerability could lead to:

• Loss of Funds if an attacker gains physical or indirect access to the device
• Exposure of Sensitive Keys in certain usage scenarios
• Degraded Trust in device security if best practices are not strictly followed

We emphasize that this is a preventable risk if users follow operational best practices outlined below.

Best Practices for Coldcard Users

Long-Term Recommendations

• Firmware Updates: Apply the forthcoming vendor patch as soon as it becomes available.
• Redundancy: Use multisig setups where possible to reduce single-device risk.
• Monitoring: Track official Coldcard security advisories and updates.
• Operational Discipline: Treat your hardware wallet as part of a broader security model, not a silver bullet.

Responsible Disclosure Timeline