Critical (9.8) in golang go. EPSS 2.0% chance of exploitation in the next 30 days. Fixed in stdlib 1.21.11, 1.22.4.
The various Is methods (IsPrivate, IsLoopback, etc) did not work as expected for IPv4-mapped IPv6 addresses, returning false for addresses which would return true in their traditional IPv4 forms.
Severity
CVSS 3.1
9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS
2.0% chance of exploitation in the next 30 days; higher than 80% of CVEs (scores of 2026-10-31)