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CVE-2021-31876

6.5 · MEDIUM

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 att…

Published May 13, 2021CWE-863EPSS 1.61%

Overview

CVE-2021-31876 is a medium-severity vulnerability. It was published on May 13, 2021 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refbitcoinops.org/en/newsletters/2021/05/12/Refbitcoinops.org/en/topics/replace-by-fee/Refen.bitcoin.it/wiki/Common_Vulnerabilities_and_Exposures#CVE-2021-31876GitHubgithub.com/bitcoin/bitcoinReflists.linuxfoundation.org/pipermail/bitcoin-dev/2021-May/018893.htmlRefbitcoinops.org/en/newsletters/2021/05/12/Refbitcoinops.org/en/topics/replace-by-fee/Refen.bitcoin.it/wiki/Common_Vulnerabilities_and_Exposures#CVE-2021-31876GitHubgithub.com/bitcoin/bitcoinReflists.linuxfoundation.org/pipermail/bitcoin-dev/2021-May/018893.html

How CyberStrike helps

Frequently asked questions

What is CVE-2021-31876?

CVE-2021-31876 is a medium-severity vulnerability. It was published on May 13, 2021 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2021-31876?

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2021-31876?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2021-31876?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-31876 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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