fontconfig before 2.17.1 has an off-by-one error in allocation during sfnt capability handling, leading to a one-byte out-of-bounds write, and potentially a crash or code execution. This is in FcFontCapabilities in fcfreetype.c.
Exploitability
AV:LAC:LPR:NUI:NScope
S:UImpact
C:LI:LA:L5.9/CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:LOther