Bitcoin Optech newsletter #416 is here:

• warns about a severe vulnerability affecting wallets generated by COLDCARD signing devices
• summarizes the disclosure of two denial-of-service vulnerabilities in Core Lightning
• describes a proof of concept for a zero-knowledge proof of reserves
• summarizes popular Q&A from Stack Exchange
• Optech Newsletter #416 Podcast
  https://bitcoinops.org/en/newsletters/2026/07/31/

If you used a COLDCARD to generate a wallet, any funds received by that wallet are at risk of theft and should be carefully moved to an unaffected wallet as soon as possible...
https://bitcoinops.org/en/newsletters/2026/07/31/#move-funds-secured-by-coldcard-generated-keys

On 30 July 2026, some Bitcoin users discovered that funds from their COLDCARD wallets had been stolen in a series of unexpected transactions on 29 July. Over the course of the day, a bug was identified in the firmware of the COLDCARD that causes wallets to be generated with insufficient entropy. As of this writing, estimated losses exceed 1,000 BTC, a figure that may continue to rise as the situation develops...
https://bitcoinops.org/en/newsletters/2026/07/31/#wallets-generated-by-coldcard-at-risk-of-theft

Chandra Pratap posted to Delving Bitcoin about two denial-of-service (DoS) vulnerabilities he found in Core Lightning...
https://bitcoinops.org/en/newsletters/2026/07/31/#disclosure-of-two-dos-vulnerabilities-in-core-lightning

fabohax posted about zkPoH (“zero-knowledge proof-of-hodl”), a proof of concept for a non-custodial proof of reserves system for Bitcoin...
https://bitcoinops.org/en/newsletters/2026/07/31/#proof-of-concept-for-a-zero-knowledge-proof-of-reserves

Selected Q&A from Bitcoin Stack Exchange

• What is Bitcoin’s objective definition of transaction neutrality?
• Why does BIP110’s decentralization benefit not outweigh its impact on transaction neutrality?
• Why does BIP110 require a 55% signaling threshold if its nodes reject non-signaling blocks?
• Why use ElligatorSwift encoding in BIP324?
• Was the OP_SUCCESSx reservation in BIP342 designed with specific opcode families in mind?
• What is the difference between the long-term feerate and the discard feerate?
• What is the quickest method for migrating a legacy wallet to a descriptor wallet on a pruned node?
• Is there historical data on orphan/stale block rates during high-fee periods?
  https://bitcoinops.org/en/newsletters/2026/07/31/#selected-qa-from-bitcoin-stack-exchange

Bitcoin Optech will host an audio recap discussion of this newsletter streaming live on X/Twitter Tuesday at 16:30 UTC.