SPIP before 4.2.1 allows Remote Code Execution via form values in the public area because serialization is mishandled. The fixed versions are 3.2.18, 4.0.10, 4.1.8, and 4.2.1.
packetstormsecurity.com/files/171921/SPIP-Remote-Command-Execution.html
packetstormsecurity.com/files/173044/SPIP-4.2.1-Remote-Code-Execution.html
blog.spip.net/Mise-a-jour-critique-de-securite-sortie-de-SPIP-4-2-1-SPIP-4-1-8-SPIP-4-0-10-et.html
git.spip.net/spip/spip/commit/5aedf49b89415a4df3eb775eee3801a2b4b88266
git.spip.net/spip/spip/commit/96fbeb38711c6706e62457f2b732a652a04a409d
www.debian.org/security/2023/dsa-5367