Auth bypass in Bitcoin
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.
Vulnerability class: Broken Access Control
EPSS: 0.016 (73.4th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L.
Affected products
- Bitcoin
- N/a — versions n/a
Weakness classification (CWE)
Public proof-of-concept exploits
References
- cve@mitre.org (Third Party Advisory, x_refsource_MISC)
- cve@mitre.org (x_refsource_MISC, Vendor Advisory)
- cve@mitre.org (Third Party Advisory, x_refsource_MISC)
- cve@mitre.org (Mailing List, Third Party Advisory, x_refsource_MISC)
- cve@mitre.org (x_refsource_MISC, Vendor Advisory)
Frequently asked questions
- What is CVE-2021-31876?
- CVE-2021-31876 is a medium-severity vulnerability in Bitcoin, classified under Incorrect Authorization. CVSS score: 6.5/10. Published 2021-05-13.
- How severe is CVE-2021-31876?
- Medium severity. CVSS v3 base score is 6.5 out of 10.
- Is CVE-2021-31876 known to be exploited?
- 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.