CVE-2020-1900: Facebook Hhvm

Critical severity, CVSS 9.8. EPSS: 1.4% chance of exploitation in the next 30 days.

When unserializing an object with dynamic properties HHVM needs to pre-reserve the full size of the dynamic property array before inserting anything into it. Otherwise the array might resize, invalidating previously stored references. This pre-reservation was not occurring in HHVM prior to v4.32.3, between versions 4.33.0 and 4.56.0, 4.57.0, 4.58.0, 4.58.1, 4.59.0, 4.60.0, 4.61.0, 4.62.0.

Affected products

• Facebook Hhvm: before 4.32.3 (fixed in 4.32.3); from 4.33.0, before 4.56.1 (fixed in 4.56.1); version 4.57.0 only; version 4.58.0 only; version 4.58.1 only; version 4.59.0 only; …

Published 2021-03-11. Last modified 2026-06-17.