CVE-2020-1898: Facebook Hhvm

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

The fb_unserialize function did not impose a depth limit for nested deserialization. That meant a maliciously constructed string could cause deserialization to recurse, leading to stack exhaustion. 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.