--- title: The safest way to store Bitcoin just lost $115 million... description: A critical vulnerability in ColdCard Bitcoin hardware wallets led to the theft of over 1,600 Bitcoin (~$115 million) from more than 7,000 wallets. The root... canonical: https://daily.dev/posts/the-safest-way-to-store-bitcoin-just-lost-115-million--yyej5mkgj twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: The safest way to store Bitcoin just lost $115 million... | daily.dev og:description: A critical vulnerability in ColdCard Bitcoin hardware wallets led to the theft of over 1,600 Bitcoin (~$115 million) from more than 7,000 wallets. The root... og:url: https://daily.dev/posts/the-safest-way-to-store-bitcoin-just-lost-115-million--yyej5mkgj og:image: https://api.daily.dev/og/posts/YyEj5mKgj.png og:image:alt: The safest way to store Bitcoin just lost $115 million... og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # The safest way to store Bitcoin just lost $115 million... **[Fireship](https://daily.dev/sources/fireship)** · 5 min read · 38 upvotes · 9 comments ## Summary A critical vulnerability in ColdCard Bitcoin hardware wallets led to the theft of over 1,600 Bitcoin (~$115 million) from more than 7,000 wallets. The root cause was a subtle firmware bug: ColdCard's MicroPython-based firmware had two random number generators with the same function name. A flag intended to disable MicroPython's weak built-in RNG was set to zero rather than being undefined, causing an 'if not defined' check to pass and the weak RNG to be used instead of ColdCard's secure one. On bare metal hardware with no OS, MicroPython's RNG fell back to deterministic inputs — the chip serial number and a timer — making seed phrases brute-forceable. Attackers looped through all possible serial/timer combinations to derive private keys and drain wallets. Victims attempting to rescue funds faced a mempool race where attackers could front-run their transactions with higher fees; the only workaround was sending rescue transactions directly to mining pools to bypass the public mempool entirely. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How did the Cold Card Bitcoin hardware wallet get hacked and lose over $100 million? A firmware bug caused Cold Card wallets to generate seed phrases using MicroPython's weak built-in random number generator instead of Coinkite's dedicated secure generator. An 'if not defined' check meant to disable the insecure generator failed because a flag was technically set to zero rather than left undefined, so the check still passed. Since the fallback RNG derived randomness from the chip's serial number and a timer, both deterministic, attackers could brute-force private keys, draining roughly 1,800 Bitcoin from over 7,000 addresses starting July 30th. _Anyone relying on hardware wallets for key security can follow RNG and firmware vulnerabilities like this one on daily.dev._ ### Why couldn't Coinkite just push a firmware update to fix the Cold Card RNG vulnerability? Bitcoin has no mechanism to rotate a compromised key remotely, so a firmware patch alone could not protect funds already generated with the weak randomness. Victims had to generate an entirely new seed phrase and move their coins with an actual on-chain transaction, and even that transaction could be front-run by attackers watching the public mempool, who would resubmit a competing transaction with a higher fee using the same stolen keys. _Developers building around Bitcoin's key model can track real incidents like this on daily.dev before designing recovery flows._ ### How did Cold Card victims protect their rescue transactions from attackers watching the Bitcoin mempool? Victims sent rescue transactions directly to a mining pool instead of broadcasting them to the public mempool. Because attackers monitored the mempool for transactions from compromised addresses and could resubmit a competing transaction with the same keys and a higher fee, bypassing the mempool entirely denied the attacker's bot the visibility it needed to outbid the legitimate rescue transaction. _Engineers dealing with mempool front-running risks can follow practical mitigation cases like this via daily.dev._ ## Community discussion Top comments from developers on daily.dev. **@bobbyiliev** · 3 upvotes > Bad year for crypto overall **@jibonkrishnaroy** · 0 upvotes > What a nice! Thanks for sharing. **@hardik15** · 0 upvotes > People are finding ways to get more ways on getting the Crypto which is deemed to be the safest option. **@documatic** · 0 upvotes > ouch... that is one nasty hack **@bob\_marley\_556** · 0 upvotes > why to store them in thirdparty sources ## Similar posts on daily.dev - [They Didn’t Steal Your Keys. They Regenerated Them.](https://daily.dev/posts/they-didn-t-steal-your-keys-they-regenerated-them--zeogglmg2) · Coins Bench · 3 upvotes · 1 comments - [Crypto hardware wallet owners face fresh security risks after recent spate of personal data thefts](https://daily.dev/posts/crypto-hardware-wallet-owners-face-fresh-security-risks-after-recent-spate-of-personal-data-thefts-cfoxbggml) · TechCrunch · 0 upvotes · 0 comments --- Tags: [#cryptography](https://daily.dev/tags/cryptography), [#bitcoin](https://daily.dev/tags/bitcoin), [#micropython](https://daily.dev/tags/micropython) [View this post on daily.dev](https://daily.dev/posts/the-safest-way-to-store-bitcoin-just-lost-115-million--yyej5mkgj) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"The safest way to store Bitcoin just lost $115 million...","url":"https://daily.dev/posts/the-safest-way-to-store-bitcoin-just-lost-115-million--yyej5mkgj","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/the-safest-way-to-store-bitcoin-just-lost-115-million--yyej5mkgj"},"datePublished":"2026-08-05T18:09:11.108Z","dateModified":"2026-09-14T07:40:54.968Z","description":"A critical vulnerability in ColdCard Bitcoin hardware wallets led to the theft of over 1,600 Bitcoin (~$115 million) from more than 7,000 wallets. 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Thanks for sharing.","datePublished":"2026-08-09T09:42:26.278Z","url":"https://daily.dev/posts/YyEj5mKgj#c-rWuzHUIwr","author":{"@type":"Person","name":"Jibon Krishna Roy","url":"https://daily.dev/jibonkrishnaroy","image":"https://media.daily.dev/image/upload/s--aTdebpqw--/f_auto/v1791865755/avatars/avatar_mPPbQk4b2aoRz5WA2Lxez?_a=BAMAMicg0"}},{"@type":"Comment","text":"People are finding ways to get more ways on getting the Crypto which is deemed to be the safest option.","datePublished":"2026-08-09T15:18:18.539Z","url":"https://daily.dev/posts/YyEj5mKgj#c-PhYOzHKHs","author":{"@type":"Person","name":"Hardik","url":"https://daily.dev/hardik15","image":"https://media.daily.dev/image/upload/s--O0TOmw4y--/f_auto/v1715772965/public/noProfile"}},{"@type":"Comment","text":"ouch… that is one nasty hack","datePublished":"2026-08-07T18:55:49.388Z","url":"https://daily.dev/posts/YyEj5mKgj#c-QpYlVThvA","author":{"@type":"Person","name":"Mr U (Documatic)","url":"https://daily.dev/documatic","image":"https://lh3.googleusercontent.com/a-/AOh14GhbmnObF755_tWGu3J4INlhcielRSd1QxYtwHHJWg=s100"}},{"@type":"Comment","text":"why to store them in thirdparty sources","datePublished":"2026-08-09T05:54:11.331Z","url":"https://daily.dev/posts/YyEj5mKgj#c-9C5N7H62Y","author":{"@type":"Person","name":"Aashish pokhrel","url":"https://daily.dev/bob_marley_556","image":"https://avatars.githubusercontent.com/u/126847212?v=4"}}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/the-safest-way-to-store-bitcoin-just-lost-115-million--yyej5mkgj#faq","mainEntity":[{"@type":"Question","name":"How did the Cold Card Bitcoin hardware wallet get hacked and lose over $100 million?","acceptedAnswer":{"@type":"Answer","text":"A firmware bug caused Cold Card wallets to generate seed phrases using MicroPython's weak built-in random number generator instead of Coinkite's dedicated secure generator. An 'if not defined' check meant to disable the insecure generator failed because a flag was technically set to zero rather than left undefined, so the check still passed. Since the fallback RNG derived randomness from the chip's serial number and a timer, both deterministic, attackers could brute-force private keys, draining roughly 1,800 Bitcoin from over 7,000 addresses starting July 30th. Anyone relying on hardware wallets for key security can follow RNG and firmware vulnerabilities like this one on daily.dev."}},{"@type":"Question","name":"Why couldn't Coinkite just push a firmware update to fix the Cold Card RNG vulnerability?","acceptedAnswer":{"@type":"Answer","text":"Bitcoin has no mechanism to rotate a compromised key remotely, so a firmware patch alone could not protect funds already generated with the weak randomness. Victims had to generate an entirely new seed phrase and move their coins with an actual on-chain transaction, and even that transaction could be front-run by attackers watching the public mempool, who would resubmit a competing transaction with a higher fee using the same stolen keys. Developers building around Bitcoin's key model can track real incidents like this on daily.dev before designing recovery flows."}},{"@type":"Question","name":"How did Cold Card victims protect their rescue transactions from attackers watching the Bitcoin mempool?","acceptedAnswer":{"@type":"Answer","text":"Victims sent rescue transactions directly to a mining pool instead of broadcasting them to the public mempool. Because attackers monitored the mempool for transactions from compromised addresses and could resubmit a competing transaction with the same keys and a higher fee, bypassing the mempool entirely denied the attacker's bot the visibility it needed to outbid the legitimate rescue transaction. Engineers dealing with mempool front-running risks can follow practical mitigation cases like this via daily.dev."}}]} ```