CVE-2021-24025: Facebook Hhvm

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

Due to incorrect string size calculations inside the preg_quote function, a large input string passed to the function can trigger an integer overflow leading to a heap overflow. This issue affects HHVM versions prior to 4.56.3, all versions between 4.57.0 and 4.80.1, all versions between 4.81.0 and 4.93.1, and versions 4.94.0, 4.95.0, 4.96.0, 4.97.0, 4.98.0.

Affected products

• Facebook Hhvm: before 4.56.3 (fixed in 4.56.3); from 4.57.0, up to and including 4.80.1; from 4.81.0, up to and including 4.93.1; version 4.94.0 only; version 4.95.0 only; version 4.96.0 only; …

Published 2021-03-10. Last modified 2026-06-17.