The mirror:// method implementation in Advanced Package Tool (APT) 1.6.x before 1.6.4 and 1.7.x before 1.7.0~alpha3 mishandles gpg signature verification for the InRelease file of a fallback mirror, aka mirrorfail.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.001
EPSS Ranking 33.7%