CVE-2018-6345: Facebook Hhvm

Critical severity, CVSS 9.8. EPSS: 1.7% chance of exploitation in the next 30 days.

The function number_format is vulnerable to a heap overflow issue when its second argument ($dec_points) is excessively large. The internal implementation of the function will cause a string to be created with an invalid length, which can then interact poorly with other functions. This affects all supported versions of HHVM (3.30.1 and 3.27.5 and below).

Affected products

• Facebook Hhvm: up to and including 3.27.5; from 3.28.0, up to and including 3.30.1

Published 2019-01-15. Last modified 2026-06-17.