CVE-2021-21708: PHP

Critical severity, CVSS 9.8. EPSS: 3% chance of exploitation in the next 30 days.

In PHP versions 7.4.x below 7.4.28, 8.0.x below 8.0.16, and 8.1.x below 8.1.3, when using filter functions with FILTER_VALIDATE_FLOAT filter and min/max limits, if the filter fails, there is a possibility to trigger use of allocated memory after free, which can result it crashes, and potentially in overwrite of other memory chunks and RCE. This issue affects: code that uses FILTER_VALIDATE_FLOAT with min/max limits.

Affected products

• PHP PHP: from 7.4.0, before 7.4.28 (fixed in 7.4.28); from 8.0.0, before 8.0.16 (fixed in 8.0.16); from 8.1.0, before 8.1.3 (fixed in 8.1.3)

Published 2022-02-27. Last modified 2026-06-17.