6.5

CVE-2021-31876: bitcoin Incorrect Authorization

Modified
Published 13-05-2021Last modified 03-08-2024

Vulnerability summary

CVE-2021-31876 is a medium (CVSS 6.5) Incorrect Authorization vulnerability in bitcoin. EPSS estimates a 1.61% chance of exploitation in the next 30 days, higher than 75.9% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 6.5, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
6.5/10
010
Medium · v3.1 (NVD)
EPSS score
1.61%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Timeline

  1. 13-05-2021
    PublishedVulnerability first disclosed.
  2. 03-08-2024
    Last modifiedVulnerability information updated.

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.

CVSS metrics

2 scores · 1 source · 2 versions

EPSS trend

Probability

1.61%

Chance of exploitation in the next 30 days

Percentile

76%

Versus all other CVEs

30-day change

No change 0.00 pp

From 1.61% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Bitcoin1 product

1 vendor · 1 product

References

5 links