CVE-2021-31876

Bitcoin Core 0.12.0 through 0.21.1 does not properly implement the replacement policy specified in BIP125, which makes it easier for attackers to trigger a loss of funds, or a denial of service attack against downstream projects such as Lightning network nodes. An unconfirmed child transaction with nSequence = 0xff_ff_ff_ff, spending an unconfirmed parent with nSequence <= 0xff_ff_ff_fd, should be replaceable because there is inherited signaling by the child transaction. However, the actual PreChecks implementation does not enforce this. Instead, mempool rejects the replacement attempt of the unconfirmed child transaction.

• CWE-863

• https://bitcoinops.org/en/newsletters/2021/05/12/Vendor Advisory
• https://bitcoinops.org/en/topics/replace-by-fee/Vendor Advisory
• https://en.bitcoin.it/wiki/Common_Vulnerabilities_and_Exposures#CVE-2021-31876Third Party Advisory
• https://github.com/bitcoin/bitcoinThird Party Advisory
• https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2021-May/018893.htmlMailing List, Third Party Advisory
• https://bitcoinops.org/en/newsletters/2021/05/12/Vendor Advisory
• https://bitcoinops.org/en/topics/replace-by-fee/Vendor Advisory
• https://en.bitcoin.it/wiki/Common_Vulnerabilities_and_Exposures#CVE-2021-31876Third Party Advisory
• https://github.com/bitcoin/bitcoinThird Party Advisory
• https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2021-May/018893.htmlMailing List, Third Party Advisory

Published

May 13, 2021

Last Modified

Jun 17, 2026

Status

Modified

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