fusermount in FUSE before 2.9.3-15 does not properly clear the environment before invoking (1) mount or (2) umount as root, which allows local users to write to arbitrary files via a crafted LIBMOUNT_MTAB environment variable that is used by mount's debugging feature.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 53.5%