ext/intl/msgformat/msgformat_format.c in PHP before 5.6.26 and 7.x before 7.0.11 does not properly restrict the locale length provided to the Locale class in the ICU library, which allows remote attackers to cause a denial of service (application crash) or possibly have unspecified other impact via a MessageFormatter::formatMessage call with a long first argument.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:NI:NA:H7.5/CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H