CVE-2018-6334: Facebook Hhvm

Critical severity, CVSS 9.8. EPSS: 1.9% chance of exploitation in the next 30 days.

Multipart-file uploads call variables to be improperly registered in the global scope. In cases where variables are not declared explicitly before being used this can lead to unexpected behavior. This affects all supported versions of HHVM prior to the patch (3.25.1, 3.24.5, and 3.21.9 and below).

Affected products

• Facebook Hhvm: up to and including 3.21.9; from 3.21.10, up to and including 3.24.5; from 3.24.6, up to and including 3.25.1

Published 2018-12-31. Last modified 2026-06-17.