The grapheme_stripos function in ext/intl/grapheme/grapheme_string.c in PHP before 5.5.35, 5.6.x before 5.6.21, and 7.x before 7.0.6 allows remote attackers to cause a denial of service (out-of-bounds read) or possibly have unspecified other impact via a negative offset.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:HI:HA:H9.8/CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H