ext/mysqlnd/mysqlnd_wireprotocol.c in PHP before 5.6.26 and 7.x before 7.0.11 does not verify that a BIT field has the UNSIGNED_FLAG flag, which allows remote MySQL servers to cause a denial of service (heap-based buffer overflow) or possibly have unspecified other impact via crafted field metadata.
Exploitability
AV:NAC:HPR:NUI:NScope
S:UImpact
C:HI:HA:H8.1/CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H