CVE-2021-21703: Debian Linux

High severity, CVSS 7.0. EPSS: 1.4% chance of exploitation in the next 30 days.

In PHP versions 7.3.x up to and including 7.3.31, 7.4.x below 7.4.25 and 8.0.x below 8.0.12, when running PHP FPM SAPI with main FPM daemon process running as root and child worker processes running as lower-privileged users, it is possible for the child processes to access memory shared with the main process and write to it, modifying it in a way that would cause the root process to conduct invalid memory reads and writes, which can be used to escalate privileges from local unprivileged user to the root user.

Affected products

• Debian Debian Linux: version 9.0 only; version 10.0 only; version 11.0 only
• Fedoraproject Fedora: version 33 only; version 34 only; version 35 only
• Netapp Clustered Data Ontap: affected versions not specified
• Oracle Communications Diameter Signaling Router: from 8.0.0.0, up to and including 8.5.0.2
• PHP PHP: from 7.3.0, up to and including 7.3.31; from 7.4.0, before 7.4.25 (fixed in 7.4.25); from 8.0.0, before 8.0.12 (fixed in 8.0.12)

Published 2021-10-25. Last modified 2026-06-17.