CVE-2020-1899: Facebook Hhvm

High severity, CVSS 7.5. EPSS: 1.2% chance of exploitation in the next 30 days.

The unserialize() function supported a type code, "S", which was meant to be supported only for APC serialization. This type code allowed arbitrary memory addresses to be accessed as if they were static StringData objects. This issue affected 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.